|I'm not familiar with "Windows AV". There is a freebie from Microsoft called "Microsoft Security Essentials" but I doubt this is what you mean. Normally Avast is fine. There is also a freebie called AVG.|
You should never have more than one AV onboard and it is possible that this is stopping Avast somehow. I would uninstall all AV's and start over. When uninstalling an AV it is best to first ensure that it is not running. If you have two disable them both before doing any uninstalls .
Finally install the AV of your choice. MSE is lightweight and effective so this might be best if your machine is a bit temperamental.
What's the time?