I would start by checking al the folders on your "C" drive to see how much disk space they are consuming. Also check the size of "Pagefile.sys", which is the Windopes swap file, and usually huge.
Somewhere you are going to find at least one folder that is consuming a somewhat ridiculous amount of disk space. "Pagefile.sys" can be relocated to another drive through the windows control panel if you know how, and if it goes in the first partition on said drive and it is a fast one, that can actually speed up your machine, because instead of having one set of read heads wandering back and forth over "C" drive, you are using two sets of read heads silmultaneously to access the requisite Data.
Re the folders, when you find one that is bloated, check inside it to see what is causing the bloat. Chances are you will find something somewhere that is unnecessary that is causing your problem.
One other thing you can do is cut all the $files in Windows, (They are backups of OLD system files that are no longer in use having been replaced by "Updates"), and paste them into your backup partition to keep a copy of them should you ever need them.