I haven't read all the replies but you need to do an “SMU reset" the way to do this varies on every machine so Google that with your machine info and you should be good to go. Also doanother pram reset if you haven't (after the SMU) and then make sure it's all charged up before shutting down again (if it's a laptop). Hope this helps. It should. I've had this happen. Its pretty common. I'm sure most peeps here have had this happen at least once. Cheers
If it's a retina model late 2012 no you cannot upgrade or remove the ram it's soldered to the logic board. If it's a non retina late model 2012 yes you can upgrade it 2 16GB with an 8GB slot in each of the two ram slots.
I have similar issues but it doesn't turn off it just screens off and on after the timeout. so it'll be off, then randomly the screen shows then if I leave it sit for 30 seconds or whatever the screen goes back off and it just does this repetitively. It doesn't power on and off, just screen turns on and off....any ideas anyone?