Check your ram.
Use another stick if you got any available. If you're using dual channel, remove 1 stick and try again. If it happens again, try the other. If this solves it, one of your ram sticks is faulty.
If it still happens, try the other ram slots. If this solves it, your ram slot is faulty.
If you overclock your cpu, try setting to default settings. If this solves it, you're pushing your oc a bit too much. Follow the instructions found in overclocker's paradise subforum. It helps.