What is a Computer virus symptoms?

After you open and run an infected program or attachment on your computer, you might not realize that you’ve introduced a virus until you notice something isn’t quite right.

Here are a few primary indicators that your computer might be infected:

• Your computer runs more slowly than normal
• Your computer stops responding or locks up often
• Your computer crashes and restarts every few minutes
• Your computer restarts on its own and then fails to run normally
• Applications on your computer don’t work correctly
• Disks or disk drives are inaccessible
• You can’t print correctly
• You see unusual error messages
• You see distorted menus and dialog boxes

Courtesy :- Microsoft Corporation
http://www.microsoft.com/security/antivirus/indicators.aspx