Interesting.
Sometimes those sorts of messages can be caused by disk/file damage issues rather than permissions issues.
So, just in case, let's try running a disk check (chkdsk) over your C drive.
Windows 7 instructions in the following document: How to use CHKDSK (Check Disk)
Select both Automatically fix file system errors and Scan for and attempt recovery of bad sectors, or use chkdsk /r (depending on which way you decide to go about doing this). You'll almost certainly have to schedule the chkdsk to run on startup. The scan should take quite a while ... if it quits after a few minutes or seconds, something's interfering with the scan.
Does the chkdsk find/repair any damage? If so, can you get an uninstall/reinstall or repair install to go through properly afterwards?