I have been a PC user for years and finally got my 11inch MBA as my first Mac. I had my MBA with lid closed for overnight. When I opened it up, there's this grey screen with a error message popped up saying something wrong with my laptop, I must hold down the power button for a few seconds then press it again to restart. It's sort of like the blue screen of death in Windows. This happened today for the first time. I'm not sure what it is. What's wrong with my MBA and how do I fix it? Thanks in advance.