I have a friend who is experiencing the very same problem. Initially he was using the X850 XT PE without any problems on a Antec SP 400 Watts. But today the machine didnt boot at all. I advised him to just plug in the CPU + MOBO + RAM + GFX CARD. Upon doing so the machine bootted but is artifacting even in Bios. I have now advised him to try a more powerful powersupply. Lets see what happenes next.