I recently had this same problem. I had bought a new WD 200Gig HD and installed it, but I could only access 137Gig. So, after much scourring I contacted Gateway Support. (Yes, I have a gateway) Lo and behold they had the answers. Seems my motherboard (read: motherboard...not software, not bios...motherboard) had a max HD Limit.
I'm no expert about all things computer related but, the answer to your problem may be there.
murat