When you start your computer up - and before you open any applications - Open Windows File explorer and enter %temp% in the address bar: (It also works if the folder is hidden.)

Delete everything you find in that folder. Don't worry - it's as the name suggests, a "temp" folder where all your applications dump temporary information and rarely clean up when they're finished. (Inventor and especially Vault will leave thousands of files in the %temp% folder.)
Depending on the age of your computer and when the folder was last emptied, there may be a LOT of files in there.
Reboot and you should be sorted. (You might also consider upgrading your hard disk if you are that tight on space.)
Peter