Recording stops before it should do?

I set my goodmans dvd recorder to record programmes and for some reason it stops by itself. there does not seem to be any pattern when it stops. i have set the time, timer, have the correct dvd etc. i have sky which works fine.
i have also noticed on dvds i have previously recorded that when i play them they sometimes freeze, then play again, missing a few scenes. Can anyone help??

Mike
May 2010