have you tried disabling fast writes? that solves issues on most boards, GF1, GF3, or GF4. (and I have your board, so i know it's there 😉) ...I'm waiting on my new PSU to truly test my new rig...5V rail was waaay too low so I powered down instantly and went to a backup system. that and maybe see if it wants the via agp 4-in-1's (it may not need em) ...older the board the less fussy, generally.
hope it helps