When trying to skype using a pay as you go modem I have a terrible picture and delayed sound. I have done the recommended sound checks and all is fine. Is it the modem? Signal? Any advice welcome

When you say Pay as you go Modem, is this broadband or dial up, as this does sound like a bandwidth issue.
Skype requires AT LEAST a 1 meg connection and more for quality video comms.

More information about your set up would be useful.