Recently, we've backed up our hard drive and placed it back into the desktop. However, when I plugged the monitor into the back, the monitor went to sleep. I've used different monitors, both graphics card inputs. The hard drive IS hooked up properly. And I've done the trick that involves holding the power button down while the power supply is unplugged, as well as the one that involves pressing f8 at the start up. The only thing that was wrong with this computer was the hard drive, that I'm trying to reformat. However, it seems like it would be a tad difficult without a monitor to see what I'm doing.
The desktop hasn't been used in about 4 months because of a defect in the hard drive.