What causes all wall receptacles in one room to stop working?

The circuit probably tripped because too many things were plugged into the receptacles or there is a short in the wiring that leads to that area. If you can find your circuit box, look to see if any of the little switches appear to be in the off position. Unplug everything from those receptacles. Flip the switch to the on position. If it stays in that position, plug everything back in one thing at a time until something trips the circuit again. (If you are able to plug everything back in, it may have been a power surge that tripped the circuit. )

If the switch will not stay in the on position even if nothing is plugged in, call an electrician. Those circuit breakers are there for safety.