Regedit my friend changed tdr delay to 8000 and now his computer is not starting

Solution
Poor choice by your friend. That essentially means his GPU could not respond for >2hours without the system worrying about it.

Computer is not starting how? Can POST/reach BIOS? Or can't boot into Windows?

Please post the full spec.
Poor choice by your friend. That essentially means his GPU could not respond for >2hours without the system worrying about it.

Computer is not starting how? Can POST/reach BIOS? Or can't boot into Windows?

Please post the full spec.
 
Solution
TdrDelay
Specifies the number of seconds that the GPU can delay the preempt request from the GPU scheduler. This is effectively the timeout threshold. The default value is 2 seconds.

TDR reg keys

so.. wonder if its sitting there waiting for 8k seconds now.

glad it was your friends PC and not your own, I was going to say don't let friends play in your registry.
think he best using win 10 installer to boot into safe mode and then change regedit value back toa default so PC will load. anything around 10 is way better than 8000
On another PC, download the Windows 10 media creation tool and use it to make a win 10 installer on USB
change boot order so USB is first, hdd second
boot from installer, on 2nd screen after languages, choose repair this pc, not install
choose troubleshoot
choose advanced
choose start up options
hit the restart button
choose a safe mode (it doesn't matter which) by using number associated with it.
Pc will restart and load safe mode
right click start button'
type regedit and press enter

navigate to whereever the value is and change it back to 2

this won't fix GPU if its broken but might let him into windows.
 
His screen just went simply black, nothing happened and BIOS could not be entered. I took his hard drive to my home, connected it to my pc and booted my pc from his hard drive. Could start the PC and delete the 8000 TdrDelay File. So I fixed it on my own, brought his hard disk back home and everything works now, except for the issues he already had. Thank you all for the concerns so far.

His GPU seems to block all his games and applications and at the very moment and he cannnot find out why. Specs will follow later in case he decides to not bring back the pc yet

Tried updating drivers, didnt work. I know the information has been very scarce so far, but any suggestions?
TdrDelay has been set to 8 now and it didn't fix his issue of his GPU blocking games and applications :s