Pen Displays like the Cintiq tablets use a power adapter to provide power to the tablet.
Make sure the tablet is connected to the unit’s power adapter and that the power plug is connected directly to an active wall outlet. On most Cintiq tablets the power cable from the wall outlet can be removed from the power adapter. Make sure the connection between the two is secure. With most Cintiq tablets the power cable can also be removed from the back of the tablet, follow the steps in the tablet’s user guide to check this connection and make sure it is securely connected.
If the issue continues, contact Wacom support. Please have a copy of the sales receipt for the tablet available as it will be needed to validate the warranty for repair.