I have a similar problem to this. I run Windows 7 and I tried to upgrade my video card after getting a new power supply in. The power supply worked fine. I used driver sweeper to clean the drivers of my Radeon 4350 before turning it off and inserting the 5770. I had to move what I think is a wifi chip around the PCI slots to fit the card. Now after the bios posts, the screen blacks out and displays either three pixels or 1/6 of the screen in green diagonal lines. I can't seem to get to safe mode either.