iMac 5K problems.

Hello.

Im having several problems with my iMac 5K(late 2015), the pc will shutdown and restart just out of blu. Also when using iMovie it won't upload videos( to YT) or share then inside the system. Other times iMovie just shutdown while attempting to share content, sometimes even the computer it self shuts down. I have the error monolog but I don't know how to post them here. I tried format the computer and also I erase the hole system before reinstall the OS and still the problems continue. I have a total of 24 GB memory install, could these be the problem ? Do I have to upgrade the memory to a proper 32 GB ? Thank you for you're help in advance.