I've also run the Disk Checking tools from my C Drive Properties Tools menu, as well as run "chkdsk /f" which runs chkdsk on boot, neither run showed any errors in the drive.
I've done this before on moving from windows - ubuntu, but it's been stuck at 100% verification for 4 or 5 hours - validating Steam cache files 0 out of 1, validating Team Fortress 2 file 1 out of 1.
I've already tried cancelling and re-validating before, to no avail.
If there are individual files you can narrow the issue down to that are not huge, try deleting them and re-downloading/verifying to see if it helps.
Restarting Steam between attempted verifications may help.
) This happened when I was trying to make Portal 2 and Stanley pabs together and I deleted some files accidentally.