Help with "Primary hard disk not found" Message

I have a Dell 500m laptop.  A few weeks ago, I turned it on and got the message "Primary hard disk not found".  I assumed this meant my hard drive was blown, but I removed the hard drive, blew out any dust from inside the space where the hard drive sits (old-school Nintendo style), and reinserted the hard drive.  The computer started up as normal and has worked since then. 

A few days ago, when I was using the computer it was making a faint clicking sound so I turned it off.  When I turned it back on, I again got the "Primary hard disk not found" message.  I've tried removing and reinserting the HD, but that's not fixing the problem this time. 

Any advice?  Is my hard drive blown?  Why did removing/reinserting seemingly fix the problem the first time?  Could it be something else that's broken (like whatever it is that detects the hard drive)?


-Shannon