If you are getting static or no sound from your classroom mic/ sound system and have checked to make sure your mic is charged and all your volume knobs are turned up, the following has helped in the past.  

Open plastic equalizer cover found on back of amplifier and note the position of the sliders (usually in the middle). With the amplifier on, move all sliders up and down several times. This may cause loud pops to come from the speakers but this is normal. When the sliders have been moved up and down several times, return them to previous position or the middle position.