How do I know if I have a virus? [1/1]

Generally speaking, a virus causes your computer to do things you don't intend it to do. Some of the more tell-tale signs of an infected computer are:
Your antivirus program is disabled for no reason and cannot be restarted.
You cannot install or run an antivirus program on the computer.
Strange dialog boxes or message boxes appear onscreen.
Someone tells you that they received an e-mail messages from you containing attached files (especially with .exe, .bat, .scr , and .vbs extensions) that you did not send.
New unexplained icons appear on the desktop.
Strange sounds or music play from the speakers.
A program disappears from the computer.