Light fitting won't work with more than one bulb in place
Your fixture is made to use a set of 4 x 4W LED bulbs (for a total of 16W), but you're trying to use 50W halogen bulbs instead.
This is extremely unsafe, because the halogens give out orders of magnitude more heat than the LEDs do, and your fixture is not made to survive all that heat.
It's a good thing that it's "smart" enough to "see" that you're overloading it and shut down instead of just work for a while before catching fire.
You need to get some GU10 LED bulbs to use in that fixture.