Inspiron 8500 power button not working

Returning to computer found blue screen.  Could not turn off computer by pressing power button - no response. Removed power cable and battery to turn off computer.  Replaced battery and power cable (battery is fully charged, power seems to be working) . Green light is blinking very slowly. No response to pressing or holding down power button. Tried trick of removing cable and battery, holding down power button, replacing cable - no response to pressing power button. No previous hints of problems. Power button always previously worked.  Is there any way to revive it?