I'm having the exact same issue. I'm getting a Required Device not found issue. & there's an error code. I think it was xCf0000000000 or something along those lines...Exactly what did you do to fix this issue. Can't run a system restore because of this. Tried from within OS boot itself via Acer's eRecovery & also Alt+F10 doesn't work at all. I think it's having trouble getting to the partition. I have no multiboot/other OSs on this drive. No externals in USB etc. Please help. I really need my system functioning as it should.