I have 2 outdoor coachlights that are sensored to go on at night that have suddenly stopped working. We've changed the bulbs and made sure they are securely screwed on but that doesn't seem to be the problem. Can it be that the sensors have stopped working and if so, how can they be fixed? Or do we need new replacement fixtures? Thank you!

In top of the ligths you should have a sensitive to light switch ,that only works when is dark ,if this unit is bad lights will never come on.
In most cases you can replaced this switch ,or maybe the whole unit.
If you know how to use a meter check the switch to make sure that's the problem

Any chance the coach lights are switch controlled from inside the house that is now turned off?