You don’t need really…
CTRL-ALT-DEL should be enough on ME to close the majority of the programs related to avast.
I really suggest you download and run from a floppy Process Explorer 8.41 and close all other programs that could be related to avast.
ashdisp.exe, ashMaiSv.exe, ashServ.exe and aswUpdSv.exe
For technical information, see: Stop On-Access Protection and Exit…no Exit ?!?. Here you will find what I told about dificulties on shutting down an antivirus: Sorry, but it’s not possible to free the memory completely - your computer may stop working. Some operations are hooked by the resident providers, your e-mail program may be redirected to the avast! resident protection module (so that it can check the mail), etc. It’s simply not possible to unload all the modules. In that case, you wouldn’t be able to send or receive your e-mail anymore, and the operating system may suffer from other malfunctions. The best thing we can do is tell the resident protection not to scan anything and pass all the requests untouched.