Hi iarp, welcome to the forum
The report file for the boot time scan is found in the windows 7
ProgramData folder
This folder is hidden, so you will have to "show hidden files..."
(an easier way to locate the ProgramData folder is to open explorer and type in the address bar "C:\ProgramData". This will open the folder)
C:\ProgramData\Alwil Software\Avast5\report\aswBoot.txt
Scott