Question : Problem: HP Pavillion is "Floating Belly Up"

HP Pavillion a500y with Celeron processor.  Windows XP  SP-2 and all available updates and patches.
This one won't boot at all.  The only sign of life is a flashing pilot light near the push button to start the thing as well as a flashing light on the back of the power supply.  

Answer : Problem: HP Pavillion is "Floating Belly Up"

The first thing I'd try is another power supply. The green LED on rear of PSU is a test (power good) LED. Should be lit continuously when PSU is powered.