Make sure that your BIOS are up to date to avoid screwy voltages. You may want to check out MotherBoard Montior 5 to assist in tempurature readings and other nifty info
. Run a Burn In Test, see if that picks up any errors. Dust your system, make sure no fans are broken, and if you have multiple things in your PCI slots, take some of the unneeded things out for a day or two and see how your system runs then.
Also, your PSU... I agree that it is low powered, however it SHOULD run your system fine! You make want to check that though, before going through all the trouble above.