After recently finding out about 12V rails and how much Amps are required on a rail to have there newer gpus run problem free....what PSU do you have Saxman? and how many Amps are you running per 12V rail??Suggested for a 4870 is 32A per 12V rail and if you want the Nvidia core 216 the required Amps per 12V rail is 36A.
sax have you considered selling your board and getting a relatively cheap alternative?
what board is it you have there sax ?