Hi. I have experienced exactly the same thing. The other day I wanted to run a full scan and it started then stopped immediately declaring nothing was found. As the original poster said, it didn't even scan. The same thing with Quick Scan. I have uninstalled and reinstalled Avast Free 3 times now. Each time I can run one successful, complete scan, and then the same thing happens. I'm beginning to suspect a virus which has not yet been discovered. I am very concerned that I may not have any AV protection now, even in real-time. Something is definitely wrong here. I'm thinking of changing to another AV app. I like Avast, but this seems like a potentially dangerous situation. I hope a fix is coming - very soon!