You tried a whole new motherboard? Did you place the new RAM, and GPU into the new motherboard? So you basically rebuilt the PC with all new parts, and it still won't boot? DID you set the BIOS up correctly on the NEW motherboard?
So, really, the problem is, you have a new PC build that won't start, right?
IN the future, ROLLING BACK drivers after a crash typically isn't a fix, unless you updated the drivers, and it crashed. Was this the case?