(when you, in fact, know nothing about computers)
If you have some kind of virus, spyware, adware, worm, etc. on your computer, and you have no idea how to fix it... try some of these steps before you freak out and go buy a new computer. :)
Disclaimer: Out of my experiences with computer problems, these are a few things I've found most helpful, but by no means am I a professional at this. I don't know how much you know about computers, so I'm going to describe the steps as if you don't know anything all, to be on the safe side. All of this stuff should work with Windows XP. I'm not sure about other Windows versions though. This guide is also partly for my own reference.
Option 1: Scan your computer using Malwarebytes Anti-Malware. Download it free from their website (google it). If you can't get to your browser from the infected computer, access it from another computer and save the .exe file to a flash drive, then plug the flash into the infected computer and copy the .exe file to the desktop and run it. Install the program and do a quick scan. If it prompts you to restart, do so. After that, do a full scan and restart if needed. Malwarebytes usually gets rid of most petty viruses. It's worth a shot.
Option 2: System Restore. This is an extremely helpful feature of most Windows computers. Go to Start -> Run -> and type this in the box: "c:\windows\system32\restore\rstrui.exe"
Option 3: Google it. Whenever I have a computer problem, and the first two options don't work, I google it. Google is a wonderful resource, and many people out there are probably having the same problem or virus that you have. If you type in the "symptoms" of your infected computer, or any virus/error messages you are being presented with, you may get lucky and find some answers on how to resolve the problem. This takes time and a lot of reading, so have patience. If you find something that describes a problem similar to your own, read up on how the problem was fixed, if it was fixed at all, and how YOU might go about fixing it. Sometimes it requires you to go into your system registry and delete the specific virus files. But this is dangerous because if you accidentally delete something you aren't supposed to, your computer could be screwed over and not work right. There are also many computer help forums that you could consult, with people who know a lot more about computers than I do. They often ask you to do HijackThis logs, which I'm afraid I've never done and I don't understand a thing about. But those people usually know what they're talking about so it's worth a shot as well.
Option 4: Reformatting. The very last resort. This is when you completely wipe your entire computer of everything on it and reinstall the operating system, thus starting from scratch. ONLY do this if you 1) Have the CDs that came with the computer which include the OS such as Windows XP, certain programs like Microsoft Office, as well as all of the drivers you will need to run your computer and 2) Feel experienced enough to handle reformatting, repartitioning, and reinstalling, etc. without a problem. There are many tutorials out there (especially on youtube) of how to reformat your computer. I have a Windows XP from 2002 and I've only reformatted it once, in October 2009. It was a real pain in the ass because I did not have all of my driver CDs, so I had to download a lot of them from the internet on the DELL website. Secondly, I lost the CD for my Linksys Wireless Adapter which allows me to get onto the internet. I had to buy a new CD off the internet for $25 to get it to work. After about a week of reinstalling drivers, etc. I finally got my computer running smoothly. But remember, this process wipes EVERYTHING off your computer. Before you do it, make sure you have a backup somewhere of important files or programs you don't want to lose, such as another computer, a flash drive, or external hard drive (preferred over a flash drive, as it is much larger. This thing is very helpful, and totally worth it to buy for the future. This way you can just save everything on that and not the computer and not have to worry about losing the files, even if you do reformat). Make sure you have all of the installation CDs for all your art programs, tablet, etc. Only attempt this option as a last resort because it is tedious if you don't know what you're doing. It's best to get someone who knows more about computers to help you.
And one last note: NEVER give up on a computer just because it has a virus. No matter what, it can always (usually) be fixed. Don't waste your money on a new computer when the infected one is fine, it just needs fixing. I know how frustrating computer problems can be! If you have any questions, feel free to ask with a comment on this entry and I'll answer to the best of my ability. But like I said, I'm not a pro at this stuff. Good luck! :)