This is what I would do.
Remove the HDD and attach it to another PC through usb . So u need a ide/sata to usb adapter. http://www.newegg.com/Product/Product.aspx?Item=N82E16812232002
Save all the files you need.
Put back the HDD in the desktop and just reinstall the OS.
See how the PC acts for a few hours and if it's stable.
I hate the repairing option. U never know how long will work.
A fresh , clean installation is better in my opinion.
I don't think there is anything wrong with the PSU, but who knows.