Din, welcome to the forums…
you may want to double check your settings for Avast!
…also let us know what OS, etc.
Did you have Norton AV installed before?
try using the search button on top of the screen with “boot scan” and you should get many results–I got too much to list here.
I use Windows XP Pro and did have Norton installed before, but un-installed everything and manually went through my registery deleting them files norton left behind.
When i click on these options it says Select Boot time scan i get several options to choose from:
Scan all local disks
Scan selected path
Scan archieve files
Advanced options (With some sub menus underneath)
But from there, there is no option to stop the boot scan complety?