It sounds like there's a fault somewhere.
With the amount of information you've given I'm afraid that's the best diagnosis I can come up with.
The fault could be with the supply coming from another room, could be the switch, could be the wiring, could be the fitting(s), could even be that all the lamps have failed at the same time.
Adam
October 2009
A wire has probably fallen out of its terminal connector - either a live or a neutral and probably at a ceiling point.
Lighting circuits usually loop from fitting to fitting with the Live & Neutral wires - if a wire comes adrift all the lights after the break will stop working and all the lights prior to the break will continue to operate.
If you attempt a diagnosis and repair yourself take great care - electricians are safer.
Good luck...
Peccavi
October 2009
I can answer this question...
The lights on our downstairs circuit have stopped working - i?