Kids, grandkids, siblings and even well meaning friends can, even with the very best of intentions "fix" our computers for us so they no longer seem to work at all. An improvement here, a change there, and before you know it the computer resembles nothing we've ever seen before. Or the grandkids come to visit and look at website they wouldn't be looking at from home and the computer gets nasty viruses on it. Either way, we've got a problem.
We get into habits with our computers, and expect them to work in certain ways. Another person comes in and sees it working not his way and wants to "fix" it, when really there's nothing wrong. Many people who know a bit about computers discover a horrible itch to "fix" every body else's computer and "help" them out by adding all the latest, coolest stuff, even though really there's nothing wrong. The itch to tamper is almost irresistible to these people, and this can be a terrible burden on the rest of us.
The other problem that some times comes about from visitors using your computer is viruses getting on to it, from those visitors, maybe, going to websites you don't normally go to yourself. These are often porn sites, though more and more now it is possible to pick up viruses from any websites. The problem is not the website itself, but that the website was hacked by another party and a virus or other malware was added to it. It is up to the webmasters for that site to keep their web pages as clean of viruses and the debris from hackers as possible. The real "fix" for such things is to adequately safe-guard your computer, by installing and maintaining the right anti-malware products.
1) Viruses: If everything on your computer seems to be basically as it was, but the computer is now working very slowly or is popping up message boxes you've never seen before, or asking for money for products you have no idea what are, then it's possible that a virus or other malware has been introduced (albeit accidentally) on to your computer. If it was the grand kids, then tell their parents to confiscate their allowance for the next year, and then try some of the suggestions here. There are also many, many (Many) articles on the internet about dealing with computer viruses.
2) Too Much Help: