Great, thank you both. I ran Malwarebytes yesterday and it found a few stuff. Spybot S&D and Microsoft Security Essentials also found some other things. I've also read about SuperAntispyware, maybe I will download it too later, just to check if it doesn't find anything else. Right now I think the only remaining issue is that the photo icons don't work, and the background is black and I can't change it. I followed some instructions from the Microsoft official website to fix it, and it worked, but now I restarted the computer the problem came back. I'm still going to restart the computer in safe mode and scan it with everything again, just to be sure. A friend recommended I download TDSSkiller to check for rootkits, maybe I will.
Weirdest thing is, I never download anything! I think it must have come from my pendrive, which I take to my university's printing room often. I can't think of anything else.
Anyway, I will try MSE for a while, since I already installed it, and if I get any trouble wiith it I will try EsetNOD32. I did play Sims for a while this morning with no problems though.