This board is for discussing and attempting to solve problems we have with our computers. The only rule we see necessary at this time is to be civil.
Please tell us all the info you have regarding your problem such as operating system, what you were doing when the problem occurred, etc. If you tell us the brand and model number of your computer it will help tremendously in finding the answer. We do not claim to be experts but we'll try to help.
Google is the best source of information for most computer problems. Almost without fail, there are plenty of people in cyberspace that are having or have had the same problem you have. Search for the answer.
The most common problem is malware of some sort. I am using this term to include rogue downloads, popups, and spyware. There are many legitimate programs to help you manage these problems. The effectiveness of these programs changes all the time so the list will change also. Currently, the best site I've seen along these lines is Securitytango. Follow their Let's Dance link and you will be able to fix most malware problems.