NXT brick not executing programs correctly I have an issue that I am hoping someone might be able to resolve:

We're using Mindstorms in the classroom as part of a STEM program, and have one NXT brick that won't execute programs correctly. The program is a simple move/turn/move program and the program works on other bricks. 

It will move forward and seems to attempt the turn but then just stops.

Working programs from other groups also don't execute correctly on this particular brick so we eliminated a programming error. 

We have tried soft reset, hard reset, and updated the firmware all with no effect. 

I'm hoping it doesn't mean we have one totally useless robot. Any help is appreciated!
There are a few options for the cause of the error. It could be at the microprocessor level, meaning that the execution of the program is wrong, or it could be at the motor driver port, meaning that the NXT tries to drive the motor attached to the specific port but can't due to some electrical failure.

The first option can be eliminated by using other forms of output (e.g. screen) instead or along with the motors, the second can be analyzed by swapping motor ports and testing them individually.

However, in any case you probably won't be able to repair it yourself, so you should contact Lego instead if the existence of the error is certain.