I have 2 Phillips DSR704's - both have replacement hard drives in them, and both are plugged into an APC UPS. At first I thought the HD on one might be failing due to the reboots until I noticed the second unit was also rebooting at basically the exact same times. Technically, there is about a 1/2 a second delay between them rebooting actually (one will reboot followed very quickly by the second). That kind of leads me to rule out the hard drive going bad in the one.
Also, this is not isolated - they ALWAYS reboot at the same time... And it's happening on a daily basis now, sometimes a few times a day.
Since they haven't been plugged in to a phone line I am trying to force a call on them both right now to see if things improve after doing so. I did notice though that when I went to do so, one reported the last attempt was a day ago and the last status was: Succeeded. Not sure how it succeeded since the phone line hasn't been plugged in for over a month - that seemed weird to me.
There has been no pixelization on either unit and both units are reporting about 43 degrees C (Normal). Both are running the 6.4a software. One has a 150G HD and the other is a 300G HD.