I've recently noticed (as in it's been happening more often) that I wil either put my mac on standby or shut the lid and when I turn it back on it will be fine for like 15 seconds. Then the screen will go dark and I have to hold the power button down to restart. It's a mid 2010 and I've upgraded to lion, otherwise nothing's changed. Any ideas? I'm going to bring it in because its hard to get class work done (teacher says put laptops away til work time and my laptop will need a restart).