Why is my Nexus turning on and off by itself?

[AC Question]

My nexus turning off by himself and on by himself

Its very weird I'll describe the problem as clear as i can be.

sometimes it getting into a "loop" of turnings off and on... it usually stops by himself in a certain point.

last time it happened I looked for a manual to get into the recovery mode. and when i'm getting into the recovery mode it actually quit from the loop. then I guess its a problem of software because everytime when it gets into is loop of turnings off and on it can be stopped by getting into the recovery mode.

problem is - when i quit recovery mode by restarting the nexus or powering off and than manually turning on the phone - it will return to his crazy loop back.

I TRIED FACTORY RESET and it wont help either!
actually when I did it I noticed something weird who might give you guys a clue :
when the "android is starting.." phase is coming, and it writes "optimizing app XX of YY" so every time the number of Apps is being changed. one time its 83 apps and then its 107 apps, and then its 73 apps.. each time it turning on and gives me another number of apps to optimize... weird right ?