Windows 7 64 bit. Was running a normal app (compiler IDE). System shutdown as if there was a power loss, but there was not... Started back up in Windows safe mode. Started up fine, but approx 2 minutes later, hard shutdown again. Waited approx 2 minutes. Started back up, went into BIOS. CPU temp at 121 degrees F (49.5 C), MB at 119 degrees F. All 3 fans running at approx 1200 RPM. System shutdown while in BIOS after being on approx 2 minutes.
Decided to open case. I see that my MB has a power button, which glows red (LED backlight, momentary on style), and a reset button. Both show power. Nothing appears wrong. Hit power button again, but now nothing happens. Tried power button on MB, but nothing. I shut off power in the back of the power supply. LED buttons no longer lit. Turned Power Supply switch back on, buttons light up again. Cannot turn on computer, either from MB button or from power button on front of case.
No new hardware added. System current with patches. Run MS Security Essentials. Fans rotate freely. Although there is some dust inside chassis, it is not excessive. System has never been overclocked.
System has a Core i7-920, with ASUS MB.
Power Supply is CoolMax CUG-950B. I note that there is a SLIGHT melted plastic smell coming from the power supply. System is approx 4 years old, and until just now, no other HW problems.
Any help appreciated.