Formatting HD > 10GB

Each time I format a HD using “format.com” I can see only 2.1GB of a 10 or 20 GB HD. I use Fdisk first then I do the format. Can anyone suggest how I can retrieve my entire 20GB space?
I tried an old DM1 program, but it splits the drive into several partitions and never sees the entire 20GB. Is there any program that can let me see my 20GB after a format?

Thanks