You may have faulty hard drive controller drivers. You can use this software to scan for any drivers you have problems with. When you installed your OS, did you have the entire capacity of both drives available?
Also right-click your “My Computer” icon and choose “manage”. Then expand storage and click “Disk Management”. Does it show the rest of the space there as unformatted space? Or does it just show the space you are seeing in my computer? If the unpartitioned and unformatted space is showing you can right-click it and create a new partition and format it there as well. They will show in my computer as new drive letters.
The possible problems with your hard disk drive is the partition created for your hard disk drive. The other space of your hard disk drive has no partition created for them. You can create another partition for the hard disk drive through the storage disk management of your computer, you can also use third party software like partition magic to safely create a new partition.