To day, I didn`t recognized that the battery was very low, so I was writing a mail. Suddenly the screen did go in black. I did think that it had something to do with empty battery, so I did connect the power. But the PC did not start as usual. The back screen comes up, and a message: No bootable device available, try to restart. (I am not sure about the exact message) I did press any key, but it did not work. When I press Esc another black screen with the message: press the arrow up or down to select a boot. That did not work. I press Power off, and Power on several times, and the same screen shows up.
But after a little while, I tried to start the PC again, and then it was quite OK 
Why this ? I have had a laptop before, and never had such problems if the battery was to low.
This PC have a 128 gb ssd with the C: system, and a 750 gb hdd