Yes, not being sure what operating system you run would place you as a beginner
There is always a chance an infection caused this, if Malwarebytes is also not working (that is what you meant by "Malware Anti-Malware" I hope?). But thats a bridge too far at the moment, could also just be random glitch. First try and get Avast! running again.
To do that, try a program repair. That is done by opening Control Panel, then select Programs and Features. Once there, find Avast! on the list, when you click on it a drop-down list should appear. Choose the Repair option, then follow the remaining steps it tells you.
I would also ask if you currently have or recently removed any other anti-virus program on this PC?