About a week ago my PC suddenly became slow and unresponsive with web pages taking 2 to 3 seconds to open. Checking Task Manager I see that 'Avast Antivirus Service is often peaking to 87% CPU usage meaning that my overall CPU usage is at 100%. Similarly I’m seeing 60%+ memory usage with Avast taking about 1,400 MB. Has anyone else seen this problem suddenly occurring - I am running Windows 10 on a reasonably fast desktop.
Thanks in anticipation.
Try the following,
[b]Repair & Clean Install of Avast → https://goo.gl/t7aJGq[/b]
Repair Avast:
Open the Avast User Interface > Menu > Settings > Troubleshooting > Repair App. > Restart the Computer or,
Control Panel> Program and Features (Add/remove program)>Select Avast> Select Repair. Reboot when completed
https://www.avast.com/faq.php?article=AVKB204
If Repair doesn’t fix the problem, try the following:
If your Avast settings are not the default settings and you want them restored after the Clean Install, follow this before removing Avast.
https://goo.gl/TXjM7h
Clean Install of Avast:
https://goo.gl/4Ptzkf
If you need additional help with the Clean Install, watch this:
https://youtu.be/p-h3myRD51A
Hi - thanks for that Bob. The repair seems to have worked. 
Good to hear.