My experience with an X1950XT wasn't dissimilar!
It would crash often and lock up. I bought this 7600, then all my games worked minus Counter-Strike: Source which had the same error.
But recently I bought a new PSU - I upgraded from a 550W Thermaltake to a 620W Corsair, and now CS:S works!
So I think my PSU was the problem all along. Going from my experience, I would say your problem is the PSU
It would crash often and lock up. I bought this 7600, then all my games worked minus Counter-Strike: Source which had the same error.
But recently I bought a new PSU - I upgraded from a 550W Thermaltake to a 620W Corsair, and now CS:S works!
So I think my PSU was the problem all along. Going from my experience, I would say your problem is the PSU
