|You said that the space in the other partition shows up as unpartitioned. |
Bear in mind that there are two possible situations:
1. The remaining space on the hard drive can show up as "unallocated". This means it is not allocated to any existing partition and neither is it formatted. This can happen if the partition was deleted in some way.
2. The remaining space is allocated to a partition but not yet formatted. This is more likely due to a corruption of the partition table.
There is a difference between these two which may require different approaches. I hope I am not teaching granny to suck eggs here.
So what you are describing could be caused by corruption of the Partition table and / or an erroneous deletion of the partition.
There is a utility called test disk that might help recover the deleted / lost partition. Test Disk is available at:
Check it out. I hope this is the answer to your problem.
☺ When everything else fails, read the instructions.