Welcome. My name is XXXXX XXXXX would be glad to assist.
Do you have the Make and Model of the fixture?
On your fixture, what terminals do you have for connections?From the wall, you have a live, neutral and ground?
You tested the live and neutral with a lamp and they are good when the switch os on?
We found the problem - in this case it was that we hadn't fixed the bulb in properly - its working now - thanks for your help