Alarm bells here.
Do a hard reset - hold the off button till the laptop turns off, wait 30 seconds then turn it on again, choose 'start as normal' from the menu.
When the laptop reboots disable Avast! - right click on the tray icon and shut it down - I think it is under All shields.
If you do not have this go on the Internet and download Malwarebytes (
https://www.malwarebytes.com ) the Windows download is half way down the page. Run it with a full scan and follow any instructions. If it finds nothing reboot and allow Avast! to load up (automatic) then right click the tray icon and click on About Avast!.
You should get an update option, this you need. Update and run as normal then do a full scan with Avast!.
As a last resort do a System restore to before the problem and then update Avast! and do the Malwarebytes and Avast! scans.