Sorry, I didn't explain clearly. Let me try again:
If Avast! find some suspicious emails (according to what I set), it will display 3 small windows one by one.
I will clicked 'Delete' button in the first window, then
I will clicked also 'Delete' button in the second window.
In the third window, the 'Suspicous Message!' window, I can click 'Continue' button or 'Block it' button. However, on cliking any one of them, my Windows XP stopped for a few minutes....sometimes even need to switch off the power(cannot do restart).
So, my Windows XP will crash whenever Avast! find virus in coming email in MS Outlook.