PowerPC not turning on

I have a PowerPC G5 1.8Ghz and when I came home today the computer was running quite loud, and there was no image on my monitor. I checked the front light on the computer and it was flashing three times, a code for memory problem so I changed the memory and now I have no light and still no image on the monitor. Suggestions? I have tried the an SMU as well?

running quite loud - it should have cooled down by now. Will it boot up off the install disk? Can u test with another monitor?

Yes, Collin Bl is right. Try booting off a disk (holding "C" while booting). You should also try a "target boot" (holding "T" while booting. Turns your Mac into an external firewire-connected HD temporarily.)