I'd run a GPU benchmark like furmark to see if the same problem occurs.
If it runs through, then try to clean up and reinstall your GPU drivers and OpenCL stuff.
If it doesn't... well if you have no spare parts then I guess I'd try putting the card in another PCIe slot. Other than that I'd be pretty lost as it could be the PSU, GPU or motherboard.
Furmark may not be a good test if your computer crashes when scrypt mining as furmark doesn't actually stress the memory that much. If you're SHA mining then furmark would probably work.