Inbox mail deleted by itself.

I have this problem. When i open my Windows mail, the first folder to go in is INBOX. Whenever i click other folder (for example, Outbox or Sent) and come back to inbox, i find that the latest e-mail i receive will be deleted. The inbox mail will keep on delete if i repeatedly go to other folder. I belive it should be because of virus/worms. I downloaded avast and latest update, and get all of my drive scanned. But the problem still there after the scan. What could be the problem?
I usually use Windows mail in Windows Vista to check mail. I can’t find the deleted mail (well, auto delete , i shall call it) even in Deleted items. The only things i can imagine this will happen is virus. But how come with latest Avast update, still can’t solve the problem? I don’t think is Window mail problem…

what’s the point of double posting that ???
http://forum.avast.com/index.php?topic=50239.new#new

:-[, no body seems can help…

doesn’t change anything to double post. Stick to one thread per topic please.