Go to the room that is without power and unplug everything from all plug outlets.Turn off any light switches.If any of the outlets are GFI ,they will have a reset button on them.Reset them Usually this type is used in kitchen,bathroom anywhere near a water supply. Go to the breaker box double check that the breaker is for that room and reset it again.If it trips instantly you may have a bad breaker,a short in the wiring or a short in one of the plug outlets.If it doesn't trip after about a minute go to the room and turn on a light switch or plug in a lamp.if it comes on and stays on breaker and outlets should be ok.There may have been too many things on at once overloading the circuit.Most electrical items are labeled how many amps of current they draw.If the items being used draw more amps than what is marked on the breaker it will trip to avoid over heating the wiring and possibly catching fire.
It sounds like you may have to much being ran for that breaker ie hairdryer, TV, VCR etc. If that doesn't work your breaker is more than likely bad.
Your breaker itself may have gone bad.