It's not hard. Whether it's fun or not depends on your point of view! At worst, it's no worse than brushing your teeth -- hey, you gotta do it. Right? At best, you learn something about your computer and gain some confidence in your dealings with the mysterious box.
1) Back Up: Unless you only web surf, you HAVE to back up your computer. One of the greatest unhappy-making events I see is the near-irretrievable loss of pictures and documents from unbacked up computers. There isn't really any excuse, either. It's cheap and easy. You can back up your whole computer for just the cost of a large external disk and some disk cloning (mirroring) software. For a 1000 GB disk and the software, that's $150. Your system will be automatically cloned once a week, once a day, or whenever you choose, at night, or whatever. You can boot from the cloned disk in case of internal drive failure. See articles about elsewhere in this blog, Bring In the Clones, and also on free on-line backup (up to 2 GB), useful for critical system ID information and documents.
2) Internet Security: You might be surprised how many systems I encounter that do not have any Anti-Virus or Anti-Malware software installed on them, or have expired subscriptions for commercial AV or IS software that isn't doing much protecting. There is plenty of free AV and security software from reputable firms, and there is not need to either do without, or pay for a commercial product. See the articles on free antivirus programs, "Free Microsoft Anti-Virus ...", and "Free Anti-Virus Software".
3) Dirty Computers: Your computer is a Vacuum Cleaner and the delicate internal electronics are the bag. Sounds good, huh? The sad truth is that many people DO NOT clean out the dust and dirt that accumulates over time and settles onto the electricity conducting parts and blocks the free passage of cooling air exhaust. I see a lot of very dirty machines and some that fail to function properly because of internal shorts, and/or power supply failure, due to dust build-up. Just vacuum out the interior of the machine once every 6 months or so, and if the dust bunnies have gotten really aggressive, reverse the vacuum hose to the exhaust and blow out the machine. Do remember to take the computer outside for this! See this article on Filthy Computers.
4) Slow Computer: Nobody likes a slow computer, especially one that seemed to be faster only a short time ago, but now seems to crawl. Slowness can be caused by a number of things; it's a symptom, not the disease. The disease can be infection by malware of some kind, perhaps a virus, many viruses, a trojan, you get the idea! (see #5 below), or it can be too much junk software installed on your computer, that slows it down. All those little icons down there on the right of your Taskbar represent busy little programs using up precious system resources. Do you really need all of them? Maybe not. Get rid of the ones you don't. Or, it may be that the computer you feel as if you just bought a year or two ago, is really now 5 years old, and just does not have enough memory to deal with the demands of modern software, graphics intensive browsers, and high internet speeds. See "Keeping an Older, Slower Computer Going ...". If your computer is 7 or 8 years old, however, the likelihood is that you need a new computer, since your CPU itself is probably too slow to keep up.
5) Infection!: OK, this is the scary one. What now? Your computer is behaving erratically, popping up all kinds of dire messages, asking you for credit card info to download bogus for-pay solutions to problems, preventing you from using the internet, and generally making you miserable. Well, however you got here, there is a way out, or ways out. Starting with the easiest, least effort solutions, you need to see if you can install some malware removal software, or boot from that Symantec Norton Internet Security CD, or download a free bootable CD image to boot from (one good one is available from AVG), and then let the software see if it can't isolate and remove the Bad Stuff. If that fails you may need to remove the hard drive and attach it to a known good virus-free system with good security software and scan the drive form that system. Haven't yet seen a system where these 2 methods will not eventually work. Take a look at the following articles: 4 Articles on Virus Removal.
Also, I do have to say, this is one area where you may need pro help, since wasting time while failing to eradicate the infection just allows the problem to get worse.
OK, that's enough for now. I'll continue this article in a couple of days and finish of the Top Ten PC Problems and How to Prevent or Deal with Them.