A. Temp files
1. Right Click on C:\ in Windows Explorer
2. Select "File Finder:
3. Type in "*.tmp" without the quotes ofc
4. When ya get the list of files, click on the date column header so it ranks them by oldest at top. Delete them in small bunches of 20 or so. It's as if to delete files, it needs empty space in proportion to the size of the files being deleted. In some cases, divvying up the load seems to help.
5. Do not delete any with dates / times newer than your last reboot.
B. Rinse and repeat with *.dmp files
C. Reboot and then try Disk cleanup again and make sure to clea up system files such as old WU and KB uninstalls.
D. Open Event viewer and delete system / application / security log files after going over recenbt days of reports and m,akiing sure nuttin that you are worried about
E. Us file finder again on *.* and this time rank by size.... see if there are any bigmuthas in there like a movie you forgot was there.
F. Cleanout and never use again any folder with a "My" in front of it like "My Downloads.
G. Uninstall programs and when you reinstall them, chnage the location from C:\Program Files to something on the HD that makes more sense.
Still a 120 GB HD has 111.76 GB of file space cause they been lying about storage size (using base 10 numbers instead of base 2 as appropriate) for about 20 years. Now set aside 15% as recommended for free space. That leaves you with about 95 GB. Now figure even astute windows users have their footprints grow to about 70 GB footprint. That leaves you just 25 GB
Of stop worrying about all that stuff leave Windows on ya SSD and get a 2 TB SSHD for gaming