Venue 10 5050 unlock bootloader - Dell Venue

How to unlock bootloader on Venue 1010? I found the thread for 7/8 but the above steps didn't work. I get not into bootloader menu by VolDown+Power, but into Dell BIOS.
My tablet is soft-bricked, and I can't boot into OS, only to fastboot.
Command
Code:
fastboot oem unlock
writes FAILED (remote: unknown OEM command)
Command
Code:
fastboot flashing unlock
simply doesn't work.
When in fastboot mode, it shows SECURE_BOOT: Enabled, so it seems my bootloader is locked. Weirdly, I can erase partitions (system, boot), but cannot flash it. It shows error flash_cmds error.
How to unlock it?

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Listen bro just try to hold power and volume down but when you see the Dell logo let go of power ...
What happens ?
If you rooted it , you used "tethered" cwm custom recovery ...
Why don't you boot the "tethered" recovery you used for root to install your backup that you dumped
Just select install .image file and install your backup you dumped that way ...
Kernel - boot
Recovery - recovery
System - system
*
Do you have a stock ROM ?
*
Use this guide to boot cwm temporarily... See if you get into this recovery to allow us to root again or flash some of your dumped images etc etc
https://forum.xda-developers.com/android/development/intel-android-devices-root-temp-cwm-t2975096

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KevMetal said:
Listen bro just try to hold power and volume down but when you see the Dell logo let go of power ...
What happens ?
Click to expand...
Click to collapse
If I press VolDown, I get into the BIOS. Usual BIOS like they have on Dell laptops.
{
"lightbox_close": "Close",
"lightbox_next": "Next",
"lightbox_previous": "Previous",
"lightbox_error": "The requested content cannot be loaded. Please try again later.",
"lightbox_start_slideshow": "Start slideshow",
"lightbox_stop_slideshow": "Stop slideshow",
"lightbox_full_screen": "Full screen",
"lightbox_thumbnails": "Thumbnails",
"lightbox_download": "Download",
"lightbox_share": "Share",
"lightbox_zoom": "Zoom",
"lightbox_new_window": "New window",
"lightbox_toggle_sidebar": "Toggle sidebar"
}
If I press VolUp, I get into this menu
This how it runs Diagnostics
And Droidboot is a simple fastboot in terms of Dell.
KevMetal said:
If you rooted it , you used "tethered" cwm custom recovery ...
Why don't you boot the "tethered" recovery you used for root to install your backup that you dumped
Just select install .image file and install your backup you dumped that way ...
Kernel - boot
Recovery - recovery
System - system
Click to expand...
Click to collapse
Just after your words I recalled how I rooted and used this way. I rooted via thethered temporary CWM. There was no permanent recovery on the tablet.
I booted again into this CWM, repacked my IMGs into ZIP, signed them but ZIP flashing failed both for signed and unsigned.
How can I flash IMG files directly via CWM? I didn't find such option. My CWM is 6.0.3.7 version.
KevMetal said:
Do you have a stock ROM ?
Click to expand...
Click to collapse
No, there is no stock on Dell support site. I found only kernel, but how it would help me? I assume I messed system partition, not kernel.
Thanks for you assistance a lot!

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First of all, it's not clear will I be able to flash my dumped backup with locked bootloader or not? If not, then how to unlock it?

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Is this a dual boot windows ?
If so you could try to install windows through a bios bootable USB
Shouldn't you turn of the secure boot in your uefi bios like in a windows PC
---------- Post added at 07:28 PM ---------- Previous post was at 07:22 PM ----------
The correct way to install android here would be to use an android OS installable via an uefi boot USB like you would install windows with a pendrive
I don't think you are gonna flash your rooted system image through uefi bios or a locked bootloader
Some bootloaders never get unlocked period .
Uefi is a bios in which you should have an option to disable uefi secure boot and that could be it but this is more PC country than Android as I've never seen an android device with this type of bios other than on dual boot setups
In which case install windows 10 through bootable USB drive in BIOS then install android as secondary OS through windows ...,....

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Is this a dual boot windows ?
Click to expand...
Click to collapse
No.
Shouldn't you turn of the secure boot in your uefi bios like in a windows PC
Click to expand...
Click to collapse
Too good to be true. There is no such option.

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Windows is signed and you could get a uefi bootable installer quite easily ..I use twrp in which you have an option to flash images ....however you still need a UNMODIFIED image to flash
Read the original thread which or where you followed the cwm root instructions and scroll down to read about what they say about unbricking
You are up the creek without a paddle since you don't have an official stock image of your system and your bootloader is locked
As a last ditch attempt start looking at windows uefi bootable recovery USB sticks as Dell offers these ...see it it one will format the file system and put windows or Ubuntu on it ....but that will only work if you find a bios setting that turns of uefi secure boot
Good luck