Are you sure that Avast is making problems, because I don’t see it’s files in the log? Do you have dual boot on your PC?
Open notepad.
[*]Click Start
[*] Type notepad.exe in the search programs and files box and click Enter.
[] A blank Notepad page should open.
[] Copy/Paste the contents of the code box below into Notepad.
cmd: bootrec.exe /fixmbr
cmd: bootrec.exe /fixboot
[*] Save it to your USB flashdrive as fixlist.txt
Boot into Recovery Environment
Start FRST in a similar manner to when you ran a scan earlier, but this time when it opens …
[*] Press the Fix button once and wait.
[*] FRST will process fixlist.txt
[*] When finished, it will produce a log fixlog.txt on your USB flashdrive.
Exit out of Recovery Environment and post me the log please.