again rebooting? so your original box was doing the same.... pretty low odds youd get two boxes with the exact same problem, I'd think.
How are you connecting to your tv? Disconnect everything but that connection to the tv and power (e.g. phone, antenna) Still rebooting?
Try a different connection to your tv.... so if you're using HDMI, use composite. (for example HDMI problems can cause weird problems like reboots... and HDMI fixes were in one of the newer software updates)
Why hasnt the software updated on the box? What version are you running?
You might even consider trying the tivo in another location on another set.
You may have electrical issues that are causing the problem... noise, open ground, etc
-Roamio Pro *Just out of the box!* :D
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-Mini Lifetime MOCA
-Comcast/TiVo Mutant dvrs - RIP
-2x Upgraded Series 2 - Retired