Alright, this is what you should check first:
At the rear of the drive there are jumper(s) which dictate which size, and setting the drive will be. With samsung drives usually you are needing (2) jumpers to use all the drives capability. On the jumper setting tag (on top of the drive), look for the jumper settings that will say (upper 32mb) and (master/slave/cable select)(which ever it is). Place the jumpers correctly on the pins ( you will use 2 jumpers) and set it for whatever position it will be used as. (master/slave/cable select). Then re install the drive, and enter your C-MOS settings, and auto detect the drive...it should now be shown as a 120GB drive. That should correct the problem.
If any other questions feel free to PM me.
Truckie
PS: WELCOME TO TECHIMO!!!