how can i fix my shower?

my shower has stopped letting hot water through it, my hot water is turned on full and the dial is turned on the hottest setting i have turned the cold water off then no water at all comes through,can anyone help. the shower is a trinitron fp?(built in)
david greaves, March 2005


done
Is there an anti-scald valve in the supply line?

Jim Coakley, March 2005