How can I fix a whole ceiling of halogen lamps which have stopped working?

most probably a loose live connection in previous light switch or cielling rose, depends where all the mian connections are, if the neutrals are connected in connector strip in the light switches is probably in the previous light switch.

who cares
February 2010

Either there is an interruption (break) in the Live supplying the two switches or the Neutral return path from the lamps is broken. Any other explanation requires multiple faults to have happened at the same time.

You should find a way of testing for Live at the switches - if not there discover why not - if there examine the Neutral return path.

It may be useful to temorarily replace a dimmer with a conventional switch during your investigations.

Good luck... Take care...

Peccavi
February 2010