No boot HP G60-214EM. blank screen, power-on button lights, occasional flash from HDD light.t?

have tried hard reset (removed battery & all external devices, hold down power-on button for 15 seconds, restart using AC adaptor etc). Have followed HPs reset procedure, problem is as soon as I plug in power supply the power on button lights without being touched(?). F10 to enter BIOS doesn't work nor does F8. There are no blinking LEDs to give a clue, no beeps, no error messages just blank screen. Any suggestions gratefully received.