If this is the case you can reclaim some (12.5GB in my case) space by disabling the windows hibernation option. This deletes the hidden system file hiberfil.sys which otherwise resides in the root of C:.
As Microsofts site is prone to link rot I'm copying the information found on their support page over here.
1. Click Start, and then type cmd in the Start Search box.
2. In the search results list, right-click Command Prompt, and then click Run as Administrator.
3. When you are prompted by User Account Control, click Continue.
4. At the command prompt, type powercfg.exe /hibernate off, and then press ENTER.
5. Type exit and then press ENTER to close the Command Prompt window.
source: Microsoft