Marg have ALL the LED's gone out or just some of them? If all of them are out it is the driver board that takes the main and makes the voltage what the LED's can use. Almost always it is something simple like a blown transistor or capacitor, or even a fuse. If you have not checked yet, check the fuse. its the easiest thing to check, however it does not sound like it from your description. You might be able to order the driver board and replace it.
DW