I upgraded my G4 500DP from Mac OS 9.1 to Mac OS 9.2.1. When I re-booted, when it got to the Starting Up splash screen (with the progress bar) the screen went black and the power light started flashing continuosly (blink, blink, blink, blink, ...). If I let it continue, most of the time, the screen would return once everything was booted and the light would stop blinking but would be brighter than normal. Other times I could only get it back by pressing the power button on the computer to put it to sleep and a second time to wake it up. In this case, the power light on the display would be off. I ended up restoring 9.1 from a backup tape and everything is back to normal. Has anyone else seen this? According to the ACD user's manual the blinking means it cannot detect a valid video signal.
Here is the configuration:
Power Mac G4 500MHz Dual Processor
22" Apple Cinema Display
Radeon AGP card