I'd have thought a System Restore would be the easiest option to look at first. Running it up and seeing if there are any recent restore points (prior to "the tampering") should only take a minute. If there are restore points available, you could give it a try. If not, you're no worse off.
I'm no expert (!), and I'm aware that it's not a magic fix-all, but it's got my PC back running on several occasions. I'd have thought that this sort of minor problem would be easily sorted by System Restore.
If any IT gurus think it isn't a good idea, and I know a few IT people at work who don't like it, I'd be genuinely interested in any explanations (knowledge is power!)