Hi, let's make it clear.
I've never heard about locking partition or drive.
By the way, are you sure that 40gb is unallocated space? If it's so, try to partition the drive by following these steps.
1- boot Acronis Disk Director. You can see your "C" partition and unallocated space.
2- choose "Create Partition". Select unallocated space. Specify the created partition size. Select the created partition type (PRIMARY). Select the partition file system. Choose the partition letter.
3- Press "Commit".
I used this program several times to re-partition my HDD. Everything was charming!
NOTE! If you use Acronis Disc Director trial, it won't execute anything. Only full version allows you to complete the operation.