sfc /scannow is often worth doing.
(For those stuck, for some awful reason, on XP, it's worth doing very frequently. On XP, this will often ask for the install CD.)
On Windows 10 (or 8/8.1, although there's no reason to run either anymore) there is another step which should be run first, and which while time consuming improves the odds of being able to do the repair tremendously.
Its:
Dism /Online /Cleanup-Image /ScanHealth
Dism /Online /Cleanup-Image /CheckHealth
Dism /Online /Cleanup-Image /RestoreHealth /Source:wim:d:\sources\install.wim:1
(the latter assuming your install DVD or ISO is mounted as D:\ )
Semi-full instructions at:
https://technet.microsoft.com/en-us/...or=-2147217396
although the exact, annoying, format of the "/source" option requires some interpretation.