I remember an issue re the M400 tablets not 'waking up' if they were in standby or after hibernating. Whilst the HD light flashed and unit appeared to be on, the screen would remain black.

Sometimes turning into tablet mode and then back to latptop mode seemed to fix it, sometimes it wouldn't.

By accident I have found a way that seems to work most of the time.

Hold down the function key for about two seconds and the system jumps back into life. I am now much more confident about putting the system into standby or hibernation mode.

Hope this helps.

mirgy