I am having some problem with my iMac. The problem is the following: I can boot the system, and use it. If I shutdown and wait some time and then turn it on again, it will not boot. I need to remove the memory and change with other form other slot to it boot again. No matter what memory I put on it, I get the same problem: The first time boot perfectly, then if it stays shutdown for some minutes, I need to change the ram from bank1/dimm0 with another. Does anyone know what problem is this? How I can solve it?