The most likely problems are: defective memory, overheating cpu or overheating graphics card. Run a stress test of cpu/memory (like orthos or prime, make sure you use all 4 cores) and see if you get any errors. You can try to open up your case and see if it takes longer to get error. If you haven't done so yet - clean your cpu cooler and graphics card. Google orthos to find how to use it.