Cant see more than 2GB of my HDD

When installing W2K Prof it only detects 2GB of my 20GB HDD. If I create the partitions in fdisk before installing, Win2K setup shows the partition as damaged and wont install. If I install Win2k on the 2GB partition Disk administrator does not detect the unallocated space, and if I create the extended partition in fdisk after the installation Win2k Blue Screen on boot up, if I remove the partition its fine again.