LED light fixture has suddenly stopped working. There are no bulbs to replace. What can cause this?

Without more details about your fixture it is difficult to be specific, but in general the weak link is the power supply unit. Note that it may be an integral part of the fixture and therefore non-repairable.

To over-simplify this a bit, LEDs like about 2-3 volts DC. The power supply module will convert your line voltage of 120 volts AC to the required voltage for the LEDs. You rarely see an LED itself go bad, but the components of the power supply wear out just like any electronic component.

This doesn't fix your problem, but I hope the information is helpful.
WallyH

Check switches and wire connectors. Pugged in a kitchen? Check GFCI