I would try running it with the bare minimum, take out the sound card, take out all the drives but the boot drive, run with just the bare essentials and the graphics card and see if it behaves normally. If it does, add back one component at a time until you start having problems. To rule out power problems, then go back to the bare minimum, make sure it is still ok, then add back the component that seemed to cause the problem to start. If it is still ok, replace the power supply. If it's not ok, replace whatever that component is.