G5 Tower chimes at start up, monitor stays black even after battery replacement

Last week I started up my G5 intel Tower and the computer ran fine, I could hear the chime and the usual noises BUT my apple cinema monitor stayed black. I unconected it from the cpu and then restarted the computer, pluged it back in and everything was fine. This week, my computer begins to boot, chimes, the monitor is black again and the compter stops start up noises after 20 seconds or so. I thought maybe becuase of all the electircal shortages paired with the fact that it is an old computer that maybe the battery (CR 2035) inside was dead so I replaced it.

Same problem....that fix did not work.

Also the not sure if this is related but the video card seems to be making a louder hum then usual.

oh and I hear the webcam get power, it is conected to the monitor via firewire.

Please help, what do I do next?

THANK YOU!