Have you been in the bios setup, and seen that your pc`s bios support the size of your disk ?
If not , you will have to use a diskmanager like ontracks or the one that follows your disk.
If it does support the size of disk, do as Daveml said or use any free util like part (free/shareware),
BIOSFDISK (free), AEFDISK v2.0 (shareware) special fdisk (free)
There are many more, but take a look at these and use them with care....