What error(s) does avast show ?
How exactly did you reinstall avast ?
What OS/SP ?
What exact version of avast ?
Any other security (related) software installed ? (or was there)

The directory C:\Windows\System32\LogFiles\WMI\RtBackup stores ETW trace files (extension .etl) for real time event trace sessions.
You can create copy of it and submit it to VT, or boot in safe-mode and submit it from there.