Twice tonight my Tivo locked up. Once it was a blank screen, and the other time it was paused on a recorded program. It was paused for a couple hours. I unplugged it and it comes up fine, but it is getting frustrating. Have any of you had issues like this before. Do I need to replace the unit? It is a Phillips series 2 and is about 2 and 1/2 years old. Thank you in advance.