Mini box shutting down

I have been having problems with mini boxes .  My problem is they keep shutting off .  This is my third box and it has now started shutting off .  I can be watching TV and the Box shuts off , sometimes it shuts off and then the power light starts cycling on and off then starts a reset cycle .  Then some times it just powers off and I have to go disconnect the power and reconnect the power connection to get it to turn back on .  I know it is the mini box because my TV gives me a NO SIGNAL box .  Some times when I turn on the TV I get the no signal box on my TV .  Then I have to disconnect and reconnect power to the mini box to get it to restart .  Like I said this is my third box this summer and they have all done this .  The only difference was my second mini box after a bit finally also lost audio out to the TV .  I know it was the box because I switched inputs to my TV between my mini box and my DVD player and the audio problem stayed with my mini box .  Like I said before now my third mini box is starting to power down .