Original post by: Wingman ,
Go to Disk Utility and verify the drive shows up in the left hand column. If it does, it should show the size and manufacture of the drive on one line, than indented below it should show the logical name. Click on the drive and select repair. It will scan the disk and attempt to repair it if errors are found. If they are found, run repair one more time to see if any errors remain. If so, the disk may be going bad.