Why doesn't Windows recognize my second hard drive?
Check the following things:
1.) Make sure all cables are firmly seated in their sockets.
2.) If you are using an IDE drive, make sure the jumper settings are set correctly to either "Master" or "Slave."
3.) Make sure your BIOS detects the drive. To access your BIOS, watch the boot-up screen for a message that says "Press this key to enter setup." Press the appropriate key.
4.) Open Windows's Disk Management console and check the status of the drive. It may need to be partitioned or formatted in order for you to use it.
For information on using Disk Management to format or troubleshoot a drive, see Microsoft's Knowledge base article #309000.