This will disable Avast but I do not feel it is the problem.
Before you run the FRST fix then do the following first
From repair my computer run the command prompt
Type in the following command and press enter :
chkdsk C: /r
If you are still unable to boot then :
Download the attached fixlist.txt to the same location as FRST
Run FRST as before and press fix
Try a reboot on completion