You need to replace your PSU. I almost guarantee that's the problem and even if its not it will be soon.
Buy the EVGA 600B: http://www.amazon.com/dp/B00EON40CS/?tag=pcpapi-20
It's more than enough and the only reason I am suggesting that over other PSU's right now is because this one is a pretty good deal at the moment. I would normally suggest the 500B for this system but it is actually more expensive than the 600B right now.