Try setting your bios to "fail safe" or something less than "optimal" that may help.
If that dosen't work, try pulling everything out except one stick of ram, and the HDD and video card. Just bare bones.
Then in Bios again, set the video to pci rather than agp, (or disable agp if you can) if you think it's video related.
Also, try booting from the CD and do a repair there.