If it comes back after uninstalling in gadgets you need to do as suggested in option 1 of my first post and that is in win7 I have done it on my win7 netbook.
Control Panel, Program and Features, Uninstall or change a program, select avast and click on the Uninstall/Change link, see image. That should display another window, select change, it should now show the avast shields and functions, uncheck the avast gadget, click Next and OK your way out.