Ask Max: Problems after installing Jaguar on G3
I've installed Jaguar on a G3 with an upgraded third-party processor, and the monitor goes black without warning so that I can't do anything but reboot the Mac by pressing the power button on the front.
I've tried two different monitors (one is an Apple monitor) in case it was the problem, but the screen goes black with either one.
Also, a new Belkin USB card I installed does not seem to work.
A monitor that blacks out can often be the result of a faulty display or video card. You have eliminated the possibility of it being a display by trying a different monitor. Now it could be the graphics card, and if you have a spare card to test with that would be a good next step. If you do not have an extra video card, do not run out and buy a new one just yet. It could well be an issue with the system going to sleep and then crashing in that sleep mode. Some USB cards can cause sleep problems as well as some USB devices. Try removing the USB card and see if the problem continues. If it stops after you remove the USB card, then you can replace the card or disable the sleep option.
This kind of dark screen crash could also come from a faulty screen saver. Disable your screen saver and the screen saver hot corners. If all these things fail to have an effect on the problem and you have updated all your software, then you should start questioning your video card.