DIAGNOSIS: This is almost always a power supply issue. No lights means the control box isn't getting electricity.
FIX: Start with the simple stuff. 1) Check that the wall outlet is working by plugging in a lamp. 2) Trace the power cable from the wall to the black control box under the desk. Ensure both ends are plugged in firmly. 3) Check the fuse in the UK plug (if applicable) or try a different power cable from a monitor if it fits. 4) Listen closely near the control box when you plug it in. You should hear a faint click or hum.
IF THAT DIDN'T WORK: The internal fuse in the control box might have blown. This requires opening the control box (a small black rectangle under the desk). Unplug everything first. You'll see a small glass fuse inside. It's usually a 5A 250V fuse. If it's black or the wire is broken, replace it with an identical one from an electronics store.
HEADS UP: Before opening the control box, make absolutely sure the desk is unplugged from the wall. If the new fuse blows immediately when you plug it back in, you have a short in the wiring—that's a job for Vari support.