Please help: Last week I upgrade my imac with 2 gigs of ram and finally installed Snow Leopard. I restarted the machine once or twice since because of software updates. I shut it off completely two days ago (I almost never do, people told me its better to let a mac sleep then waste power on a new startup a few times a day). Anyway, my wife turned on the computer today and the screen stays grey with a NOT symbol on it (you know, like the ghostbusters symbol) and it just stays like that. I'm at work but wanted to know what I should do to fix this when I get home. Any ideas or is a trip to the mac store in my future? Thanks in advance for your help.