Before you go out and purchase a new power supply, check that you don't have any bulging or burst capacitors on your motherboard. A visual inspection of the motherboard is easy enough to do to see if this is an issue. See the linked Image
That being said most motherboards that have burst capacitors are from two things, heat buildup and/or unstable voltage. Basically if your motherboard has burst capacitors and you don't see a huge pile of dust buildup or notice failed fans, then your power supply is most likely the reason your board has decided to call it quits.