There are numerous ways to wire a light, and until someone with a qualification who knows what to look for, you could be there for days.
It could be something as simple as a broken switch mech, but from your discription, it sounds like theres more to it. It could even be damaged cables and need a re-wire.
Im an electrical apprentice and although i can get a basic idea of what is wrong and what to look for from your discription, It is very dangerous you yourself doing the work.
Electric shocks can, and nearly always are, pretty nasty.
Your life is worth more than a call out fee for an electrician
Jake
December 2007