|In diagnosing same problem for a friend's Compaq Presario P8657E, have learned that apparently the blinking power supply LED light indicates a problem with the power supply or a component. Not going off after unplugging is due to the residual capacitance (circuits that act like tiny batteries) that's enough to power the LED for a few seconds.|
These are the best diagnostics I've found
In brief, it looks like a steady light means all is well and flashing light means there's a problem.
Disconnect EVERYTHING from the motherboard, including the main power connector, then plug the power cord back in to the power supply. Light should not flash.
Unplug power, plug internal power connector from the power supply (PSU) for one peripheral in. Plug in power. If light flickers a little then comes on steady, component is okay.
Repeat with each component. If the LED flashes instead of going steady on, that component has a problem.
The last connector to try is the main motherboard connector (P1). That's where mine started flashing. I thus conclude the motherboard was fried by the power outage.
Hope this helps.
If anyone has different results, please post. I could have misinterpreted something.