First the draws are prevented from falling out when opened by arresters, clips on top of draw side that have to be depressed to release the draw from runners. Take a look at a draw above/below the offending draw to check arrester positions.
You may find they are the type on the draw back two screws one each side in slotted holes slacken and slide to opposite side of hole to release draw from runners, just pull the offending draw out as you would to open but hang on to both sides of the draw they aren't light, well mine aren't.
Re-fitt the offending draw ensuring both sides are on the extended runner arm.slide draw on runners and re set the arresters before closing the draw. Hopefully it is not the runner broken I doubt you would get new one. hope this helps. It's a pain in the butt but they do this occasionally.
Bob
February 2010