Freezing picture on Thompson DT16300?

Can any one please shed light on this one ?

When watching a channel any channel after 3 or 4 minutes the picture freezes and the sound goes off, sometimes the remote will let you change channel, but you get a blank screen othertimes the remote does nothing. Plus I have a problem that I saw on another forum : in the last couple of days, when recording it records the 'time buffer' set but not the actual programme !