Do you live in an area with heavy industry nearby perhaps? Do your lights flicker sometimes on a night time? If so maybe your in a bad area for power surges. It might be worthwhile investing in a surge protector plug extension.

Also with power supplys you generally get what you pay for. Try an enermax or similar quality psu. I have a 350W enermax psu in my server that is going strong after over 3 years running far more hardware than is in your computer