What does it mean, power interruption 
I could not see my driving time/rest with this on…
It means there’s been a power interruption, ie battery disconnected.
You can just press ok to clear it and get the usual display back.
As Dav1d said the power has been interrupted either because the batteries been disconnected or because of some other power to tachograph fault, press OK to clear the message.
If it keeps happening you’ll need to get it checked out by someone who knows what they’re doing, which will probably mean a visit to a tachograph centre.