Comp has trouble identifying new harddrive?

Screwed up XP on my old harddrive. Got a brand new harddrive.

Initially had some difficulty getting the computer to recognize the new hard drive; I had apparently plugged it in to the wrong slot on that cord, if memory serves. Switched the plugs, worked fine.

Installed windows. Successfully slaved the old harddrive to the new one, where I could use both in windows XP [Old drive became "F:\"]. Started installing a handfull of things, namely drivers and a couple games. Was running fine for about a week. [If it matters, it was largely still running during that time, with a handfull of shutdowns due to having to install stuff like Direct X.]

Ten minutes ago, I decide I wanna play morrowind, which is located on the old drive. Exited out of the game I was playing, went to My Computer... and the slaved drive wasn't there.

Figuring it was a glitch, I rebooted the computer, only to find out that it isn't recognizing the new hard drive again.

Attempting to reinstall windows [again] reveals that windows is in fact still there on the new hard drive, which doesn't make much sense to me; how can BIOS not know what's attached to it, yet XP can read from it?

Anyway, I have two questions;  one of which being WTF.

The other question is... well, I was told to delete the windows directory on the old harddrive. I didn't.

Could having the old instalation of windows on the old [slaved] drive messed with the installation on the new drive?

For point #3, your motherboard may have 2 IDE busses.  Usually their plugs are side by side on the motherboard.  Just make sure your hard disk chain (i.e. the cable, with hard drives attached) is plugged into the first one.  There should be a tiny, embossed "IDE0" or something by each plug.  Just examine them and determine if you're on IDE0 of there's an IDE1 (or IDE1 if there's an IDE2).

BUT ... as you said, neither show up in the BIOS.  Reboot and go back into the BIOS just in case that BIOS type is the "save-first, list-later" type.  But it seems likely you have a conflict.

Let's try this again from a different angle.  This is troubleshooting so please bear with me.

TRY: Assume master/slave produces a problem.  (Hey, I've seen some weird sh*t like this before.)  Re-jumper both drives to Cable Select, and put the new drive at the end of the cable, etc.  See if the BIOS sees them now.

OR: Assume cable is bad.  These cables are fairly common; get another one and try the previous steps I outlined.  See if the BIOS sees the drives then.

OR: Screw putting them on the same IDE (if you have 2 IDE busses).  Put the new drive as Master on the 1st IDE, and put the old drive as Slave (just to be safe) on the 2nd IDE.  (You might have to disconnect an extra DVD or CD to make room; for the purposes of troubleshooting, that's acceptable for now.)  See if the BIOS sees them.

Now, your XP problem ... if Windows is prompting you for which OS to boot, then I can only conclude that you installed XP on the same hard disk twice.  Is that (new?) drive partitioned correctly?  Confirm it has only ONE partition, which I assume is NTFS.

Let us know what happens.  This is rather fun.