iMac powers on and gives startup chime. No display.

I am servicing an iMac G4 that starts up and makes the chime, but shows nothing on the display. There is also no video on an external display with the minivga - vga adapter. Also, the USB will power a mouse, but a keyboard does not work when attached. Unsure what to check next.

crwdns2893858:0crwdne2893858:0 crwdns2893862:0crwdne2893862:0


crwdns2889612:0crwdne2889612:0 0


Have you tried holding the on button for a minute?