LOL
Ok listen up:
Press ctrl+alt+del. Open task manager. Go to the "processes" tab. Look for anything suspicious there, eg. a process that uses too much of your CPU like 20 or more %. Note that the "System Idle Process" doesnt use any %. Just ignore this.
Anything that uses too much of your CPU, and you dont know what it is, try to find it (Windows Search), and scan it with an Antivirus prog.
OS means Operating System. Sorry but almost everyone knows that...
Now another important thing you should do, is to open msconfig to look for suspicious programms (potential viruses) that may be running at the start of Windows. Windows by default has many programms running at startup.
How to:
Click "Start" at left bottom side of the taskbar, and open the "Run" window. If you have vista or Win 7 it might be somewhere else. What OS do you have?
Once you open it, type "msconfig" inside the box (without the "). This will open msconfig. Go to the "Startup" tab.
Look for any programms seem suspicious to you, or you simply dont know what exactly they are doing.
Note that there might be something important there, so you should not haste to disable anything you dont know what it is. If you can make a post with a list of anything there is in your Startup, in msconfig, I would be happy to tell you which ones to disable (or leave enabled).
Questions?