Dear friend caught in a strange fault, machine came for windows installation, changed mode from uefi to legacy display gone.
re-flashed bios machine earned, display came as normal but when ever you change bios mod from uefi to legacy, the display will be gone.
Decided to install window in uefi mode but secure boot is enabled and you can't disable it.
Things which have been done.
1. Bios from official site has been merged and written.
2. complete bios from forum has been flashed.
3. I/O controller it8987e has been replaced and reprogrammed.
now don't know what to do .Request to masters kindly assist me on this issue.
thanx in advance

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Posted after 15 minutes 12 seconds:
Any suggestions???Please

Secure boot is still enabling?

You may try to disable it, if you set supervisor password. U try this?

thanks for your reply, yes i tried after enabling the supervisor password the secure boot option came up but what will be the issue? by just changing the mode display is disappearing.

May u turn on integrated video and try to boot from uefi/legacy?

I think, the problem with your videocard. In legacy mode all devices init by the BIOS, UEFI mode init your devices not fully. When OS Driver start init your videocard, your "display will be gone"...

but mine one is UMA(intel-builtin graphic) not shared. if this is the case than most probably processor(FCH). what's your opinion??

May u connect monitor to ur laptop?
IMHO: if u connect monitor and video signal is turn-on, I think your built-in graphic not working correctly.

p.s. i have one question for you: did you disassemble your laptop, may u broke power supply screen?

External graphic

Hello, thanks for response and sorry for belated reply because of other repair jobs , want to update the progress as you people suggested me some options.
1. First of all, as from DuMoH4er and MSF113 for external graphic check, and i have checked on extrenal VGA output it gives display properly on external.
2.DuMoH4er asked to check LVDS as i correctly understand, So for this let me explain the problem again, the display only and only goes blank if in bios setup you convert from UEFI to Legacy mode
3. Except this, all works great even you install HD graphic Drivers and play videos on hours, don't makes any problem
4. Now i have tried many options but no luck any other suggestion is welcomed.
Thanx in advance.

Maybe some minor differencies in BIOS versions or EC firmware cause this - you may try to flash other versions. Other than that - video chip abnormalities, as already mentioned.

Many Different EC, Bios version has been tried and TXE region has been also cleaned.