Click Start -> Control Panel -> Administrative Tools -> Computer Management -> Disk management and see if the drive shows up there. If it does, you may just need to assign a drive letter. If it doesn't, reboot and go to the BIOS setup and see if it shows there. If it doesn't, the drive isn't properly installed. If that's the case, I'd remove the drive, get myself a $30 enclosure, put the drive into that and plug it into a USB port where it should work if the drive is intact.
`
Good luck.