Windows Security Alerts?

I just downloaded avast! free antivirus a few days ago on my netbook, and now there’s a program called Windows Security Alerts on my taskbar that wasn’t there before, saying that avast! is turned off when it’s working fine. I’m running Vista and don’t know why it’s there since I don’t use the internet for very much. I’m running a scan with avast! right now, but it doesn’t seem to be picking anything up…

“avast! antivirus is turned off. Click this balloon to fix this problem” is what it says on the balloon, popping up from a red X on the taskbar.

I know that’s not much info, but can someone possibly help me? I’m too scared to click on anything now.

First remove every other av that is on the system.
Secondly, perform a clean installation of avast.
Instructions for it can be found in other threads on this webboard.

First remove every other av that is on the system.
General: Uninstalling a third-party antivirus software http://www.avast.com/en-eu/faq.php?article=AVKB11#artTitle