But, if, I reckon you are using Windows 8.1 instead of worrying about your expired Avast, remove it & use Windows Defender, the GOOD security built right into your OS. Once Avast is removed, WD will be on by default. Fully auto, free & no expiring or keys to renew. If your OS is Windows 7 then, drop Avast & get MSE, instead.
Also, recommend installing Malwarebytes & running it periodically. You will find many use these same 2 things.
And, btw, the people advocating MSE (Microsoft Security Essentials), that is Windows Defender in Windows 8/8.1. Same thing different name.
Look @ the chart. It fully supports what I & others have said.