Calgar, you may want to first try just opening the drive bay on the side and pull the drive out, then put it back in. In all likelihood, however, your drive will need to be replaced. Considering your system is most likely out of warranty it would be cheaper to buy a new drive (it uses regular 2.5" SATA notebook computer hard drives) and put that in yourself.
You can get some good deals on these drives on eBay (got myself a 160 GB for close to $100) or from online sites such as New Egg.