Hi rockybrian and welcome to MyCE.
The Pye PRV 645 is made by Philips and is basically a version of the Philips 610.
So try following the full factory reset procedure below taken from the Philips website.
[B]1.[/B] Disconnect the DVD recorder from the power outlet.
[B]2.[/B] Wait 30 seconds.
[B]3.[/B] Press and hold down STANDBY-ON button on the front of
the recorder while reconnecting to the power outlet.
[B]4.[/B] Release STANDBY-ON button when â€œIS THE TV ON?â€
appears on the display. All the information stored in the
memory (programmes, time) will be cleared. Complete the
first installation again and reset any items you have adjusted
during your use of the recorder.