I think your student has probably unwittingly denied permission to the recorder to access the microphone.
Depending on the browser there are two places permissions need to be granted. Flash will show a permissions dialog which can be reshown by right clicking over the recorder and selecting "settings" or "properties". Chrome and other browsers may have their own permissions dialogs which will be shown after flash tries to access the mic.
Other things to check might include that the microphone is plugged in, or if there are multiple microphones in the machine, that the correct one is selected. (again right click ->settings and choose the microphone tab ).
Occasionally it is necessary to mess with the microphone tab settings there to spark the microphone into action. I do not know why. Flash is a black box in that regard.