What version of avast do you have, the latest is 4.8.1169, see about avast for the full details ?
What errors are displayed, e.g. why won't it load, what does or doesn't it do ?
Stopping the resident protection from the tray is only good for that session and when you reboot it will start again, so there is something strange going on as what you did won't stop avast on the next boot.
Probably the most important question, why don't you want avast not to start on boot ?
avast is a resident scanner and is designed to start on boot, it isn't an on-demand scanner.