I have 90GB of C drive space left but when I try and shrink my C?
That depends but likely your page file or hyber file is near the end of your disk. You can try disabling hibernation/sleep turn off paging to disk, run a defragment/optimisation and see if it will let you shrink it more, if it lets you shrink great, just remember to turn things back on when your done 10-Jan-2021 edited: to fix spelling