i open the windows security center and find thatmy antivirus is not switched on i tried to turn it on but nothing happens

JW, February 2010

Try un-installing the anti-virus product and re-installing it. (You may need to reboot. You may need to see if the manufacturer has a special uninstaller program. Some AV products don't uninstall that easily.)

I've seen this on my machine and it was solved by re-installing.

Frank Bebo, February 2010

You don't say which anti-virus product you are using, so it is difficult to help you.

Jay, February 2010