This happened to me in the last month, same exact symptoms. After some discussions with a Cox tech it was decided a new box was the answer. No problems since the switch.
Same thing yesterday morning and this morning with the DVR box! Yesterday it was a blank screen and this morning there was a message that something went wrong during boot. Both cases after few power cycles and boot attempts it finally worked. We also have a fifth independent non-DVR box since the DVR box only supports four including itself, and this morning when we turned on the TV it was sitting on the "Welcome" screen and after one power cycle it worked! Since this thread indicates that this has been happening to so many different boxes lately it can not be a box specific so no point calling a technician or swapping the box. Cox has to figure out what went wrong on their side and fix it!
