Make sure your hard drive controller drivers are up-to-date. I had a customer's PC one time with the exact same problem, and by just simply updating the controller driver it read the correct amount of space without ever having to reformat.
They had a PCI Promise Technology
card that their hard drive connected to.
If you didn't build your computer, check your Manufacturer's website for your appropriate drivers. If there is an update for hard drive controller, it will more than likely be there.