My C Drive has 500 GB of free space, but shows only 54mb free to partition. I am unable to create a new partition of 100 GB. I also ran the defrag and still the same issue.
I am having windows 8, and using its own partition app.
Firstly, try to remove the unwanted applications that are installed on your computer. Secondly, check if there is any useless data stored in your C:\Users\<USERNAME>\Downloads or C:\Users\<USERNAME>\Documents location (<USERNAME> is the name of the user account that is used to log on to the Windows.
If the problem persists, try any third-party Windows optimization tool such as Ashampoo WinOptimizer. This tool will automatically remove the duplicate data scattered at different locations of your hard disk, and will optimize your hard disk.
Before you can create a 100Mb partition you have to reduce the size of the 'C' Drive. This will create Unallocated Space which can the be used to create your new partition. Windows doesn't like changing C, so download and run EaseUs Partition Master http://download.cnet.com/EaseUS-Partition-Master-Home-E...
Go to the Main Screen and select C.
Simply move the slider from right to left until you have reduced C by at least 100Mb
Create your new partition in the Unallocated space you now have and apply. As C can't be altered with Windows running, the changes will be completed on restart.