almost sounds like something of a compatiblitiy issue, but looking at your hardware I wouldn't think you would have one. I would try and clear your cmos again, go into bios, and check all your settings if you can.
dfi nfII ultr infinity/asus p4s800
amd 2500xp m/p4 2.6
ati 9600/ati 9600 pro
512mb pc3200/512mb pc3200