|If you have Skype it might be that (it hangs about). In which case right click the Skype icon in the tray and use Exit. If it cures the issue then there is a way to make a Kill icon with a batch file which you click before shutdown.|
If it isn't Skype then Google for UPHClean. This is a freebie from MS that stops programs hanging about so long. It even "helps" Skype to close more quickly by providing a Window. UPHClean is worth having onboard - it normally runs without intervention and does not consume background resources.
Always pop back and let us know the outcome - thanks