Hi, welcome to the forum.
There isn't really enough info of the type needed to make any kind of diagnosis, here, but there are some things of a general nature I can post which might help.
Plus some questions to narrow it down a bit.
Things.
-Download
MBAM (a good demand scanner. Blue download button.) Install it, update it, run a quick scan. Get it to remove anything found. Post the log.
Run a disk cleanup. (Programs>accessories>tools.)
Questions:
-What is your operating system?
-What version of Avast Home have you been using?
-What AV (antivirus) was installed before Avast?
-What other security programs are installed?
- Have there been any virus alert messages? If so, the virus names please, and the location/filename where they were originally found.
-Any other strange behaviour? (redirects/popups/uncommanded scans etc).