Unplug it and leave it off for 5 mins. Check that the fuse in the plug (if you are in UK) is OK and then plug it in again.
And I assume you have checked that there is power in that plug (by plugging something else in to see if that works).
If there is power in that plug, the fuse is OK and turning it off and on again as above doesn't sort it, then you almost certainly have a fault in your Qb.
best
David
