I believe it has SOMETHING to do with Virtual memory. See here.
We can do some cleanup.
Click Start> COMPUTER> right click the C Drive and choose Properties> enter
Click Disk Cleanup from there.



Click OK on the Disk Cleanup Screen.
Click Yes on the Confirmation screen.



This runs the Disk Cleanup utility along with other selections if you have chosen any. (if you had a lot System Restore points, you will see a significant change in the free space in C drive)
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This step will remove all cleaning TOOLS we used, it'll reset restore points (so you won't get reinfected by accidentally using some older restore point) and it'll make some other minor adjustments...
This is a very crucial step so make sure you don't skip it.
Download DelFix by Xplode to your DESKTOP. Delfix will delete all the used tools and logfiles.

Double-click Delfix.exe to start the tool.
Make sure the following ITEMS are checked:

• Activate UAC (optional; some users prefer to keep it off)
• Remove disinfection tools
• Create Registry backup
• Purge System Restore Points
• Re-set system settings