Thomson DT16300 pvr - Juddering and jumping picture and loss of sound?

My Thomson DT16300 pvr is not recording properly. Sometimes it cancels preset programmes altogether. Sometimes it freezes and I have to switch off from the plug and switch back on. Now all the programmes I've recorded judder and jump on playback and the sound keeps cutting out. I've had to delete all programmes from the library and start again. Luckily I can catch up on the computer, but who wants to sit at a computer all night! Can anybody please help?