Really weird PC problem (updated)

[Y2Ant]

Right, i'm building up this other PC to give to my little cousin, and it has everything it needs, but there is no floppy disk drive in it. Seeing as how i'm using the FDD that originally came with that PC, and seeing as how I have never once used it since I built this PC, I thought I would take it out of this PC, and put it in that one.

Simple enough idea really eh? Well not quite.

See, this PC has to be a complete bastard when I do this, because I can't get the FDD out since one of my hard drives is in the way, so I remove the HDD, then remove the FDD. I put the hard drive back in, turn my computer on, and… it doesn't boot. Nothing at all, just a black screen, nothing happens. Turned it on a few times, nothing.

So I put in a different HDD to make sure it's my HDD that is the problem, and voila it works. Now this HDD (from the old PC) has Windows 98 on it, and it is a FAT32, my drives are both NTFS, one with Windows XP on it, one is just files, and I can't access either of them from Win98, i'm guessing because of the different file systems. The PC recognises the HDDs when it boots up, so there is no problem with the jumper settings and whatnot.

Anywho, last night I just decided too put the HDDs back as they were, and turn the PC on again, and it magically works, the PC boots up fine as if nothing had happened, and everything is back to normal. Although originally I booted in safe mode (since it said Windows didn't start properly last time I booted it up) and all this spazzy text came down the screen so I just reset and booted normally, and it worked.

It has been running fine since, apart from one instance this afternoon where the PC just shut itself off (black screen) and did the whole black screen on bootup again, I left it for a couple of minutes before turning it on again and it works, and i've had the PC on since.

Anyway, after all that rambling, what does it sound like I have done to my hard drive? It's obviously a physical problem, since nothing went wrong until I removed it from my PC and put it back in, could it be that I put the wrong power plug in? I had two that I could have used, and forgot which one was plugged into it, so I plugged one in at random, they are the same, but one has two wires going into each of the 4 bits of the plug (red, brown, black, yellow I think) but the HDD I used with Windows 98 on it worked with both, so I dunno if it would make any difference.

The only other thing I can think of is that I somehow scraped/banged/damaged part of the HDD, the part where you plug in the power cable SEEMS to be a little wonky, but I dunno. All my data is fine so there is no problem there, I must just have somehow damaged my drive.

Is there anything else that could possibly cause a problem like this?