Welcome to the forum.
Can you tell me what version of Avast Pro you are using and are your Avast definitions up to date?
Are your MS Updates up to date?
What other security software do you have on your machine
currently and previously?
What made you suspect that you had malware?
Do you have anything sitting in your Avast Virus Chest now?
If you open the Avast GUI > Scan Computer > Scan Logs > look for the Boot-time log...what does it say (give me a screen shot or type it out if there is anything there).
Update your Avast definitions and run an Avast FULL scan. Please report back with your scan results and the answers above and I will continue with additional instructions. Thank you.