I'm no PC tech or anything, but I've been building and trouble shooting my own computer for many years now. My family has a lot of computers and for some reason, everyone comes to me when something isn't working. Even my brothers, who should be more savy than myself, end up asking me how to fix their computers. They've done schooling, but for some reason, I guess they just fall out of the loop of things. I even know their computers better than them, and they're the ones that put them together!
Most computer issues I end up dealing with these days are just spyware and adware making systems run slower or even just messing up the entire operating system. So, it usually means a reinstall, not that it's completely necessary all the time, but that's usually the easiest solution.