BIOS doesn't find HD, and computer keeps locking up.

[Dulled by Excess]

First, you could try setting up the drive manually in the BIOS, by entering in the drive's parameters. The drive's parameters are usually on a sticker/label on the hard drive itself. You'd want to take the drive off of AUTO (in the BIOS), and set it to USER and enter in the drive parameters. If your machine doesn't have any problems keeping time, it's probably not a battery issue. If you recall booting your machine, and it stopping at POST with the message "CMOS Checksum error - defaults loaded", that would indicate a problem with the battery (either that, or your CMOS has been flashed/cleared). It's not a jumper issue, if your jumpers were incorrectly set on the hard drive, it wouldn't be found at all. If you still have these problems after manually setting up the drive in your BIOS, then I'd recommend calling up the drive manufacturer and requesting an RMA.

As far as the machine locking up, that's a trickier problem. Unfortunately, it's also one that can't really be answered without more information. What OS do you have installed? Have you installed any new hardware or software prior to these problems occurring? Do you see strange error messages when this happens? When it doesn't?

Hope this helps.