Suddenly started running SUPER slow and now monitors won't come on at startup.

I was installing software for a new piece of audio equipment when the installation started taking forever. It said "about one minute remaining" on the installation but that took nearly 15 minutes. After the installation there was a mandatory restart. Upon restart my monitor did not come back on. I did a force shut down and tried again. Same thing. I tried this over and over but no luck. I then switched over to a different video card. It is a GEforce GTR 580. I hooked it up via VGA to DVI adapter. IT WORKED! Well, so I thought. My monitors came on and I began just using the computer as I normally do...but EVERYTHING was running extremely slowly. Every action required a long pinwheel wait. I ejected the installation disc from the previously mentioned software and decided to just properly restart the computer. And of course...my monitors decided to not come on again. Now I started trying everything. Different VGA cables, different power supplies, different monitors! AND FINALLY...it decided to work. Strangely enough, it worked with the original configuration. Old video card, old monitor. I can not explain why.

Well, I woke up this morning and tried to turn the computer on. Surprise, surprise...the monitors are not turning on. Sometimes the keyboard still works (as i can engage the capslock key to indicate it's working) and other times it's not. I am just wishing someone might have some insight on it.

It's a 2009 2x2.8gHz Mac Pro with 16gig of ram. A couple internal HD's and an external 9gig Raid. Running OS X Lion.

I think we can rule out the video cards. Try running Disk Utility from your startup disk and verify the hard drive you were using at the time. Another thing that comes to mind is the power supply which may be acting up. Anyway, we have several of our members who are more familiar with the inner workings of the Mac Pro, so hang on for more opinions.

Still hanging on for more options. lol. I ran disk utility. every disk is OK. When I finally had it on..everything was extremely laggy. Every action required a pinwheel wait. And after just trying to do a simple restart...my monitor won't come back on again.