Unfortunately, hard drives aren't quite Plug&Play. When it boots up, does it detect the hard drive itself? My guess is that you have a jumper/BIOS problem. First of all, look at the drive itself and see if the jumpers are set correctly. The correct settings should be listed in the documentation or, if you haven't got the documentation, check if there's a key printed on the drive, and check the manufacturer's web site. The drive should be the master and should be attached to the primary IDE controller. If that all seems to be in order, watch the computer boot and see if it displays the right information about the drive (almost all BIOSes display some information about the IDE/SCSI devices that are connected at bootup, usually something like a brandname (or GENERIC) and the size/speed. Then go into the BIOS (usually you hit F1 or something when it says something like "Press F1 to enter the BIOS" during bootup. The BIOS should have recognized the drive. If it hasn't, try tweaking the BIOS settings to try to make it recognize the drive. Remember, it has to be the master on the primary controller for the OS to boot off of it. Anyhow, I hope this is helpful.