Are you measuring the voltage between live and neutral?
If so try measuring between live and earth and see what you get (your RCD may trip if you have one).
Turn off the power and check the connections that you messed around with when you were putting in the kitchen lights, and make sure the wire which goes from the kitchen to feed the hallway light is in the right place - I suspect you have moved it so now it isn't.
Adam, August 2009
