system
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A friend of mine had about the same problem as you did except he couldn’t even boot into safe mode. I think one of the updates isn’t liked by Avast which results in the freezes you’re experiencing.
EDIT: My friend told me he had a definition update for Windows Defender with KB915597 prior to the crash. Maybe Avast marks that update as malicious for no reason and causes your computer to freeze. Could you try uninstalling that update and then reinstall Avast to see if it works?