hmm make sure you have last Bios ver...and that your CPU/Chip set are not overheating. You can run Everest http://www.lavalys.com/products/everest-pc-diagnostics
you can find tests under tools.
If it pass you can try "burn in test" for example...it will run multiple tests at the same time. Tell us how it go.
Personally i think you have saboteur at your house.