Server Hard Drive out of Space.

My server is running 2008 R2

The total space on my "C" drive is 232 GB the remaining space is now 0 bytes.

Using WinDirStat I can view that 204.1GB is under and UNKNOWN category.  But I can't seem to do anything with these UNKNOWN files.... 
The only thing I can see from WinDirStat is that they are .cab files (Cabinet File).

Can I remove some or all of them without messing up the server?  And if so HOW can I accomplish this?

Thanks for the help!