|Time and again we see threads with basically the same topic: Someone's computer has started running really, really slow, and they want help fixing this.|
Cue the hordes of good and bad ideas. The problem is that this is pure chaos; it's impossible to tell the good advice from the bad, and so the problem can easily be made worse. With this thread I'm hoping to consolidate the good advice in an attempt to keep people from accidentally destroying their computers completely.
Why do I have to do any of this?
Your computer is not made from or powered by fairy dust. It has flaws, it can break. The internet is full of people with nothing better to do than write programs designed to break as many computers as possible.
These days you don't even have to do anything to get infected with a virus; I still remember when I thought I could install Windows XP, then go online to download some protection. Before that download had finished, the machine was full of crap. It's that fast.
So in order to keep your machine healthy, you need two things: A firewall (which mainly prevents unwanted access to your computer from other computers) and an anti-virus (which mainly scans all files your computer handles to make sure they're not about to infect you).
Since Windows has come packed with a firewall of its own since Windows XP Service Pack 2, we'll take care of that later. Your main concern really should be getting a good anti-virus. The market is full of offers, some obviously better than others. Some are free, some cost money. I'm gonna steer clear of the ones you have to pay for to avoid being labelled an astro-turfer. Besides, I have no personal experience with them.
With a delightfully ironic name for the people who want free stuff, Avast! remains my personal favorite. It doesn't take up a lot of resources, it's fairly unintrusive, and in my experience Just Works(tm). It can be downloaded (free) from http://www.avast.com/
Many people swear by ZoneAlarm for keeping hackers out of their machines, and I can't say I blame them. With a fairly intuitive interface and good documentation, ZoneAlarm is a firewall that Just Works(tm) - do you see a trend here? While Windows does have its own firewall as stated above, it's not a very safe one. The choice is yours, but it can never hurt to stop by http://www.zonealarm.com/ to have a look.
Anti-virus and firewalls are only as good as the people sitting at the keyboard. If you keep trying to get infected with a virus, no amount of protection is going to help in the long run. So here's a few tips:
Don't go to sites that common sense tells you are risky. If they're offering you something that's too good to be true, it is too good to be true! End of story, that's the way it is.
Do not click links from people you don't explicitly trust. Distrust everything. If someone messages you on MSN or similar, even a close friend, asking you to look at a linked picture, don't click it. Ask your friend to confirm it's really him and not an automatic message. Chances are your friend has a virus, and if you click the link, YOU have the virus. That, or someone else has your MSN password. Both are bad.
Do not agree to install programs you don't know why are being installed. Ever. Same goes for 'screensavers with cute cats' - screensavers are basically programs and one of the oldest ways of infecting PCs that still work.
Get rid of Internet Explorer. Since Internet Explorer has the biggest market share, it's also the most targeted browser for malware - the catch-all phrase for viruses, popups, spyware etc. Start using either Firefox (http://www.getfirefox.net) or Chrome (http://www.google.com/chrome). Both are very good browsers that only take a few minutes to get used to.
Perform periodic maintenance of your system. This one can't be emphasized enough. No matter how much you protect it, no matter how careful you are, no matter how quickly you apply patches and updates - stuff slips through the cracks. Fortunately we should be down to the smaller things now if you've followed the advice so far.
There are three programs I will recommend here, each excelling in their own fields.
Spybot - Search & Destroy. This one takes care of pretty much anything sitting in the dark corners of your system listening for what you do, telling other people about anything from your surfing habits to the passwords for your bank account. Get it at http://www.safer-networking.org/ and let it run once a month or so.
Ad-Aware. Got popups that just won't go away? Then you need Ad-Aware. Anything that sits on your machine with the intent of showing you advertisements whether you want them or not gets swept away by this gem. Get it at http://www.lavasoft.com .
CCleaner. If your computer is still running slow as molasses, chances are it's a more local problem. CCleaner shines here, clearing up all the dead ends in your computer's registry, fixing all those little things left behind as programs are installed and uninstalled. Get it at http://www.ccleaner.com .
Sometimes the above things are just not enough. Sometimes a machine is so royally hosed the only real solution is to start over. If so, make sure you backup everything you're going to miss (that usually means the entire contents of your Documents directory), and either take it to a professional or reformat and reinstall Windows. Make sure to follow the advice here from the beginning of your fresh install, and it will hopefully be a one-time event.
You are of course welcome to ask around for more advice before doing something that drastic, but keep in mind - not everyone who answers knows what they're talking about; they just like to think they do.