Just to add my words of caution to Pauli's advice - dll utilities are one of the common vehicles for installing junk on your system and can come loaded with it. Read carefully before downloading and during installing to try and avoid creating more problems than you solve.
There are some basic repair routines which can scan your system for common errors and missing system files but your larger question of "can windows be repaired" is a bit like asking if a large complex engine can be repaired. The answer is ultimately yes but beyond the basic routines which I mentioned at the start more complex problems are generally best fixed by a full reinstall as the investigations and analysis involved would consume more time than the repair - and you can never be quite certain you've sorted it all.
...beyond the basic routines which I mentioned at the start more complex problems are generally best fixed by a full reinstall as the investigations and analysis involved would consume more time than the repair - and you can never be quite certain you've sorted it all.
Quite so. I've sometimes used days to find out the problem, but in the end a reinstall was needed. It would have been time saving to go for reinstall directly.
One of my favorite themes is, do partition your disk in at least two: one where you have your Windows plus some essential programs, could be like 80Gb; then, have your personal files, archive like, in another partition or perhaps, another disk, maybe even an external disk = USB. That way you can replace the engine of the car, without loosing the wheels - don't know how wise that sounds...
I've always advised maintaining op system and installed apps on one partition and all user data, backups etc on a second. Your analogy of replacing an engine without having to touch the rest of the car is a good one, especially if you have taken the added precaution of maintaining backup images of the system drive on the data drive using something Acronis which meansyou would not then have to reinstall all the apps for a recovery.