I have a Powermac G5 Quad running 10.5 and it stalls on startup.

I get the apple logo, it flashes blue, then black, then blue with cursor and stalls. I've reset the PRAM, the hard drive works fine (tried another drive and does same thing), and run /fscky? without any change. I can startup in safe mode just fine. I tried also reinstalling from OSX install disc, but aparently my disc is corrupted as it stops during install with an error message I can't remember right now. From what I've read so far, it seems that the video card could be the problem, but is there any way to be sure before I drop that kind of cash? Thanks in advance for the help.