Someone in my accounts

Hi lately Ive been seeing a lot of action in my accounts things being changed and emails being sent with just my name no subject or text usually to be returned by mailer daemon or no such address. it even seems as though someone is using my fb account to send messages. avg isn't picking up on it' and malware detection software did grab a couple of files but it still seems to be there even though i deleted a bunch of suspicious looking files.
win 7 ultimate on dell inspiron 1300 also my audio controller disappears every time i log out

any help will be appreciated thanks elliej