Here is my setup:
amd 145 sempron /asrock extreme 870
2x1gb kingston ram
700watt gold rated power supply
The rig will mine perfectly on all four cards for a few hours and then become unresponsive. I had originally thought it was a power issue and went ahead with replacing it and then the rig ran fine for awhile until it did the same exact thing. The power supply I purchased, temporarily, was a 850watt bronze rated, which should be enough juice for what I have. I then began to suspect it being a riser cable that I use for 2 out of the 4 cards. Sometimes I would boot up and it would only hash at half the rate or not see the card at all. I isolated which card it was and indeed it was one of the cards on the riser to a 1x pci-x port
It would run perfectly fine for days-weeks on 3 cards mining full blast. I got replacement riser cables and the half hash rate problem went away and all four cards were mining for approximately 12 hours. I have switched back to my original power supply but it still wont run more than half a day with all four cards going.
Is it just my power supply or can someone offer a better explanation? Any help will be greatly appreciated.
edit: I run all the cards at 960/300, which has been flawless in the past.
I have also swapped the cards around so I think all the cards are fine.