Avast won't close

Hi. I have avast trial running on my macbook air. It has since expired. Howver, i'm getting a window advising me that the trial period has expired and that I need to register the software. No matter what I do the window won't close; it is even stopping the 're-start/re-boot' process. I've had it with Avast now, this program is hijacking my system. Anyone has an idea on what I can do????

Here's a LINK to the Avast Mac forum and some answers on how to uninstall Avast. If you don't find what you're looking for there, just post a question to them.

I would personally suggest you uninstall Avast entirely (following chscag's direction link) and forget about an anti-virus. They aren't needed on Macs.