windows security alert

I have just downloaded the free version of Avast 4.6, all seems to be running ok except windows security alert keeps telling me that Avast is switched off and rec that i switch it on. i must be a bit of a thicky cos i cant work out how to do this - help ! ???

Hi and welcome george,
If you have doubts that your Avast isnt working correctly , check taskmanager (control/alt/delete) processes for the four lines indicated below. If you cannot see them then somethings wrong .

Welcome George, do you use any other antivirus in your computer?

Can you try to repair your installation?
Go to Control Panel > Add/Remove programs > avast! antivirus > Remove. Then choose Repair function in the popup window (Repair). You must be connected to the internet while repairing.

If this does not help, can you uninstall / boot / install / boot again?