Using windirstat it shows 30gb for c drive, but 20 is missing

Run a Disk Check.

Check the System files condition: SFC /SCANNOW Command

Other Troubleshooting Steps for Windows 7 to go over your install thoroughly.

i suspected something was up because when i would delete files large gigs it would not free the space
i uninstalled rollback rx and boom 30gb was now freely available

programs suck

Good work for persevering!

Stick with System Restore and Backup Images, which save many troubled Win7's we see here.