Put in your anti-virus protection. Update the protection until there are no more updates. You may have to restart the computer after udates to get more to install.
Install the windows updates. Go to start , programs , windows updates. Restarting may be required after updates and before it will install more updates.
Avoid problems by never clicking on pop-ups. Free things are risky, it wouldn't be there unless someone is making money from it. If in doubt DON"T CLICK IT ! Music - videos - movies - games may be infected. Use common sense , if its a movie in the theatres now then it is risky to download. If its a game that is for sale in the stores , then its risky to download it. Some sites will want you to get a flash player to see thier content, the link for the flash player may be a virus. It is safer to get the flash player updates from trusted sites. Allways look at the web adress from searches before clicking on it, or you may end up somewhere unsafe.
Backup things that are important to you. If your hard drive fails you may not be able to get any of it back. Even new computers have hard drives fail. Set a restore point after installing printers and programs to avoid having to redo them in case of problems (see help and support). System Restore can help by bringing the computer back to certain dates (restore points) if you run into problems.