The pooter got sad again

See, I wanted to take the hard drive from my old computer and put it in the new one. But then I realised that I was having some slot and cord match-up issues, and decided it would be easier to just burn stuff to disk and transfer it over that way. Thing is, the cd-rw stopped working in the old computer. Never fear though, I decided to temporarily move the cd-rw from the new computer over to the old one briefly, for the duration of time it took to copy stuff. When finished, I moved it back to the old one. Very simple process. Thing is, now the computer starts, but the monitor, which still gets power, doesn't show any sign of connecting to the computer. We've tried tightening everything, but still no luck. Also, when I plug in my mp3 player, no sign of being connected to the computer (though it does get power and acknowledge the computer's presence). The computer, in sound and light, looks like it is on and doing what it's supposed to be doing. However, since the monitor won't connect (and I've tried connecting another monitor to no avail) I have no way of knowing what the problem might be.

Seems the most obvious thing is that something got loose in the process of me removing and adding back the cd drive. But, I tightened everything, and everything looks ok. Maybe something shorted or died magically? Everything still has power, though. We tried moving the video card around to see if that was the problem, but unfortunately, both of our computers were too old to have the proper holes for it. Yuck. I just don't know what to do about this, it's rather frustrating!