Sony M4 Aqua Freeze?/Brick - Sony Xperia M4 Aqua

I think my device is pretty much done for, I suspect some hardware related issue, but maybe some of you wonderful people here (if there still is anyone here) could still help me.
So somehow my M4 Aqua suddenly bricked without my interference, I had been using it regularly in the morning and at noon time, when I wanted to check on it, it simply wouldn't turn on or display anything at all. Even after pressing all the buttons for a considerable amount of time, no reaction occurred, the screen remained black. When I forcibly shut it down using the button next to the SD card slot, I seem to could get it on by using the power button, but the device doesn't seem to boot at all. All it displays is the Sony Logo, no bootloop, just the Sony Logo even for hours, presumably until the battery runs out.
Yes, my phone was rooted (using files from maybe this or this guide, can't really remember) even though I haven't been taking advantage of it, all I basically did was automatically denying SU permission for Link2SD which I had installed. I also should have the custom TWRP recovery, but I cannot access it, it leads to the infinite Sony Logo every time. As I initially rooted the device, I had to flash a new stock firmware which might not be suited for my device. (I honestly had no clue what my exact model was, if it was a E2303 or E2306 or whatever, but didn't bother much since the new firmware worked just fine for months)
Even when I simply want to charge the device, the generic battery symbol won't appear anymore, instead being also replaced by the aforementioned infinite Sony Logo. If I unplug the USB, the red LED light and the Logo persists which lead me to think that the device somehow freezes mere seconds after startup.
I have also noticed that the M4 Aqua takes suspiciously long to force shut down, I have to press the little button for ~15 seconds for the screen to go black, when it really should be about 5. I have thus removed the back case to fasten the process by removing the battery directly. (Did that break something?)
I can connect my phone in fastboot mode to the PC, but it seems to freeze yet again. I can perform various actions in Flashtool, but it doesn't seem to affect the M4 Aqua, when I try to restart the phone into system for instance, Flashtool doesn't report any errors, but nothing happens to my phone. Just how the red LED persists, the blue light does too when disconnecting from the PC until I forcibly shut down the Xperia.
Flashing a new firmware is not possible as neither Flashtool nor Xperia Companion recognize the device in flashmode even if the green LED clearly lights up. Like the other LEDs, this one also persists after disconnecting from the PC. I have been using Flashtool Version 0.9.32.0 first and then downgraded to 0.9.23.1 since that one came with the firmware I had installed, but to no use.
All this leads me to suspect a hardware issue, likely with the RAM (both sticks failing simultaneously) as I gathered from other threads and posts on the internet that that is a problem with the M4 Aqua. The CPU overheating is also an often cited problem, but I think I can rule that out. I have tried to cover the back with my hand absorbing the heat, slightly bending the phone and even put it in the freezer, but nothing changed at all. I have removed the SD and SIM Card to check if they were faulty too.

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Since you opened the rear casing from the device, can you find anything unplugged or odd inside the device?

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No, at least to my inexperienced eye there is nothing in particular. (Maybe you could distinguish anything on these poor quality pictures.)
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I have noticed, however, that there seem to be connectors on the case itself, but pressing the case harder from behind doesn't yield any different results.
The red cable is responsible for the display, as it won't turn on once removed. The phone won't do anything (no vibration, no display) once the blue cable is disconnected.

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Can you try to not boot it with the sd card installed in the device? I had a similar issue but in a different phone and when I remove the sd card, it boots just fine.
Also it doesn't seem that anything is out of place in any of those photos.

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As I have mentioned in the original post, I have already removed the SD card and also SIM card, but it still refuses to properly boot.

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Since it tends to freeze when using flashtool, can you try disconnecting and reconnecting the charging port or inspect your cable to see whether the cable is the culprit since I also had the same issue regarding connecting to flashtool.

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Nope, I've tried two different cables and every other USB port my PC has to offer, it's still not connecting.
I have noticed something however while charging my phone up. (The Battery was completely drained since I wanted to check if something would change if I just kept the device running) While on low Energy (I was also charging with a different cable), a generic low Battery symbol appeared occasionally. The red light also behaved as it should, turning off when the phone was unplugged. Flashmode as well as Fastboot were naturally unaccesable though and after the battery was charged a considerable amount, I ran into the same issues.
Unless you meant the USB port of the phone itself, that one I haven't touched yet (I haven't removed the screws, but it doesn't seem too disconnectable anyway).

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Have you installed drivers for flash tool application? Because without those the device doesn't connect.

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Yes, I have. I have just reinstalled them from the Flashtool-drivers.exe in the Flashtool files, still same behavior. Connects in Fastboot, but not in Flashmode.

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Then can you try installing cubbins android 11 ROM for this phone? You need to have fastboot drivers and adb installed, but if it does manage to boot, then there is a good chance that you can revert it back to stock and also having your flashmode function working again. Not sure if it works, but do give it a try

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Hm, everything is able to flash successfully except "boot.img". Seems like the boot sector is inaccessible, I get the following error:
"error: Couldn't parse partition size '0x'."
Edit:
Nevermind, using
fastboot flash:raw boot boot.img
I was able to successfully flash it too, however it still doesn't seem that anything has changed.

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can you boot into the OS at least?

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if it booted, then you can use fast boot to flash TWRP and from there wipe everything (except internal storage). Now try to see whether it can boot to flash. If it doesn't boot in to it, then try wiping internal storage I guess? And if that also doesn't work, I'm out of options to fix that issue, probably it was a hardware issue in the first place.

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Yeah, the problem seems to persist. I have left it on for over an hour now and my phone still doesn't show a sign of booting or more than that Sony Logo on a white background at least...
Even if you couldn't solve the issue, thank you very much for trying to!
It isn't too big of an issue, I was hoping to save some internal data, but much of it is on the SD card anyway due to the very limited internal storage of my device.

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Mimi1001 said:
Even if you couldn't solve the issue, thank you very much for trying to!
Click to expand...
Click to collapse
Your welcome

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I have a similar problem with my ex-phone, it was practically unusable after installing a rom that screwed up my existence, almost everything stopped working, and my pc doesn't recognize the fastmode, I can't flash the original rom or anything like that. If you know of something that could help, would you do me a favor!

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Same issue here. The phone suddenly refused to boot. This is not after flashing anything to the phone. I haven't modified the software in the last x years. I was running stock with root. As soon as it boots, it freezes.
Flashmode does not respond, the pc does not recognize any devices is being connected.
Fastboot is pretty similar. However, the pc promptly picks up fastboot from being connected and then disconnects again. I tried like +/-20 times with fastboot and was able to get it run fastboot -w (once) and then flash Cubbins A11 but no change. I had to type all commands at once. One by one didn't work, it disconnected after the first command you execute (if you get the chance to execute a command).
I still had a TWRP recovery on there but no button combination or command let's me boot to that. It freezes at the white Sony logo. There is also this 3 button press and hold combination where it vibrates 1/1/3 times if you hold it long enough. It does not seem to affect anything.