Recently i am observing this issue, don't know whether it is Game issue or Console/PSU issue.
This happened after i started plaing AC - Brotherhood. When i start my console for the first time for that day. Everything looks fine, hear those sound multiple time which we can hear once CD is inserted(some kind of default sound for few actions). After few minutes, without any notification/warning, TV gets dim and suddenly complete console is OFF. middle LED (power led) on console blinks for few 2-3 times(green color). Once i start it again, everything is working fine.
Does anyone has already reported this if this is related to a game?, i might update this thread further as i have completed the story and moved to AC-Revelation. Hoping not to see this issue. I am pretty sure, it can't be PSU as it works well in later stages.
P.S: i have kept all auto-shut down settings OFF.