Whenever troubleshooting possible hardware problems, and because everything inside the case depends on it, one must always
actually verify (and not assume) they are providing good, clean, stable power. As a certified electronics technician, I never assume the power supply is good, even if a brand new, top-of-the-line model from a highly reputable maker.
You need to swap in a known good supply and see what happens - if for no other reason than to verify your current supply is good.
It is also important to verify your PSU is receiving good power. So every home and every computer user should have access to a
AC Outlet Tester to ensure the wall outlet is properly wired
and grounded to Earth ground. I recommend one with a GFCI (ground fault circuit interrupt) indicator as it can be used to test bathroom and kitchen outlets (outlets near water) too. These testers can be found for your type and voltage outlet, foreign or domestic, (like
this one for the UK, or
this one for German outlets) at most home improvement stores, or even the electrical department at Wal-Mart. Use it to test all the outlets in the home and if a fault is shown, have it fixed by a
qualified electrician.