This morning my Macbook Pro (2011 model), decided it didn't want to boot, and is stuck at the grey screen. The startup chime happens, but then stays on a blank grey screen. This seems to be for no apparent reason, as both OS's were working fine yesterday. I haven't installed any updates on either OS for quite some time.
I have tried several key combinations: Option, Safe-Mode, PVRAM Reset – none seem to work. I've also tried to boot from my Snow Leopard disk that came with my Macbook, as well as trying to boot from a Recovery USB Drive created from Lion.
I have BootCamp (Windows 7 x64) and OS X Lion installed.