Power Mac G4 cutting out

[TheVallog]

I know this is whiskery technology now but I'm trying to get my trusty old G4 Quicksilver 933 back into service to run some of those OS9 apps I used to love and there's a weird problem. Machine turns on and boots up normally but after two or three minutes (haven't yet timed it exactly) it cuts out to black screen and unresponsive keyboard/mouse with On/Off button light on Apple Cinema Display blinking rapidly. At that point holding down power buttons on display and front of tower won't do anything so only 'fix' is to disconnect power lead and start again.
I'm guessing it's some kind of thermal issue but anyone have any clues?

 

[Raging Dufus]

Does the tower itself shut down? Or only the display turns off?

If you don't hear the fans rev up in the tower, and/or if the tower doesn't shut itself off, it's probably not a thermal problem with the tower. It could be a thermal (or other) problem with the graphics card, which provides not only the display signal, but also power to the display (assuming you have an old ADC Cinema Display for the Quicksilver).

A sequence of flashing lights can indicate various problems, depending on the sequence, but in my experience the flashing light would be on the tower itself, not the display. Then again, I've never owned an ADC Cinema Display, so I can't say for sure.