TIVO keeps restarting

For the past three days my Sony SVR 2000 has restarted itself several times - sometimes every five minutes! It does this when I am watching live TV and when I am watching a recorded program. Also, on some recorded programs that I have made, it only records a partial program. I have used an up-graded hard drive kit (164 hours) since the beginning of the year without problems, until now. My TIVO is in a well-ventilated area and the temperatures run in the low 30s. I have tried making extra daily calls and un-plugging and re-plugging in the unit. Nothing has helped, any suggestions? Thanks in advance.