Tough BSOD to determine... It could be heat related, software related, or hardware related.
Start by downloading HWMonitor and post a screenshot of your temps here.
If your temps are fine... My last recommendation still stands - back up your data and reinstall your OS. If you have Win8 install disc + key, go for it. It'll be loads better than Vista is anyway. Would be a good idea to make sure you can find Win8 drivers for all of your components before reinstalling the OS, though.