I'm not sure what's wrong but you may be about to loose the HDD if it is faulty. Backup anything important you have on the HDD before you do anything else.
Go into your BIOS and make sure the HDD is set to 'Autodetect' Make sure all the cables to the HDD are secure, at both ends. If that doesn't help you need more help than I can provide, sorry.
Once again: BACKUP EVERYTHING BEFORE IT'S TOO LATE.