I have a hard drive that the BIOS no longer recognizes. It was working fine, but now it no longer appears in Windows. I checked in the BIOS and it is now there. BIOS will not even find it.
Have you updated the BIOS firmware recently? Even if not, check whether the BIOS's auto-discovery of disks has been disabled.
I assume you've also checked the cables connecting the drive to the system are ok?
Hold it next to your ear and give it a little shake. If you can hear anything rattling or scratching, that is a pretty good sign the drive is bad. You might also want to smell it. Burned up electronics have a very strong distinctive smell.
One thing you should try if you suspect the drive is bas is to freeze the drive overnight. Wrap it up in a plastic bag and put it in the freezer. The next day, quickly remove it and place it in your PC before it thaws out. It may boot. If it does, try to transfer any data that you do not have backed up onto a blank CDDVD or a flash drive. You may be able to get another 15 minutes of life out of the drive.
Wow, really? Why does putting a broken harddrive into the freezer help? I just stumbled over this and you certainly got my attention :D
I suspect its internal, and may have died. Open up your computer and touch it, see if you can feel the disk spinning on when you power cycle the computer. If its not even spinning, more than likely it has died.
As Josh says, you need to provide some more details before we can advice you anything. In particular, please let us know whether it's internal/external drive and the connection method used.
You left out some information that is important like if it's internal or external, USB, Firewire, IDE, SATA, etc, but I will try to give some troubleshooting tips here.
-Check the connections on both ends. Disconnect and reconnect, even if it appears secure.
-Try a different cable.
-Try at a different connection point... IDE/SATA slot or USB/Firewire port
-Test the drive on another computer.
If none of the above works, chances are, there was a physical drive failure.