Also, use CCleaner to remove any left over registry keys, etc. Use the search function on your computer and put in the search box the name of your old anti-virus, to see anything comes up that needs to be removed before installing Avast. It only takes one registry key or anything else that may cause Avast not to install properly. It may take a little more time, but I rather make the time and make sure nothing is showing up from my old anti-virus.

If you have any questions or need help, please feel free to post back.

Thank you for using Avast and have a great evening.