No Power, No boot

First, booting became unreliable, sometimes yes, sometimes no. Later, noticed battery LED stayed solid red, unreliable booting problem continued. Still later, no boot ever (black screen, no lights, no sounds), and noticed no power LED and no battery LED, with or without power connected and/or battery installed.

The battery *was* charging, I assume it's dead by now. Green LED on power supply brick is on, I assume but am not certain it works. Tried ATX reset (15 sec power button hold, no power or battery), mentioned on this site, no joy.

Would appreciate ideas as to how to diagnose and/or fix.

Thanx!