I got a used computer from my friend, he says it was working when they last used it, now no display

[Jacaba]

I got a used computer from my friend, he says it was working when they last used it, I took it home and plugged it in and turned it on, everything lights up and all the fans turn, but when I have a monitor (it works as I am currently using it to write this) shows no display, the message I get indicates that it is in fact receiving a signal but that the computer says its in power save mode. I have uninstalled and reinstalled the dvd drive, hard drive (plugged it into my current computer and it ran) all four of its ram sticks (all 1 GB, and all are functional) it's graphics card, and the card reader, all of wich work fine when plugged into my computer. I am hoping to set this computer up at the children's shelter I work at for them to play games on. It's a dell pc, not shure wich one it is, I'll add its model when I am done with my work. So far here are the specs of the computer (from the parts I have removed) 4 GB RAM, 640 GB ROM, medium graphics card (pc is very thin so it must have come installed as the friend is not a tech), 150-250wt power supply (again hard to remember right now), core 2 Intel duel procesor, don't know the motherboards make(probably dell), have tried 6 monitors on it and get the same message as above. The labels say it is running windows vista, unknown service pack. Please help.

 

[RealBeast]

Which video connector are you using, VGA or DVI?

If DVI, insure that it is the correct type DVI as they come in different types.

Does it have the video connector on the motherboard back panel or is it a separate PCI or PCIe slot?