Water just stopped coming through shower head?

Ive got a Galaxy Aqua 3000 shower and like i said it was fine for 2 minutes then no water. Power is going into main switch (the one outside the bathroom)cos the little red light is on, but no lights on shower consol,actually there are only two,one shows off/on and the other is auto reset. I cant understand why power stops at main switch and no water. Ive taken the front off and it all looks in order to me. But then again im not a plumber or a sparky. Karens answer mentioned pressure release valve, i wouldnt know where to start to look for it. I havent got a bath so i,m stuck and starting to smell. Please help. Thanks Debra Spinney.