What is broken with your cards ^?
Fans ?
The FANs are new... The cards froze the PC after 1~5 minutes... The 3 cards isolated have, at first, the same problem...
Have you checked for burnt out caps ?
I have a 5850 I am working with one of the caps burnt out, it would boot up fine and play some games but most of the time it would freeze the PC.....
Trying to solder a new cap on..