You probably have a thermostat problem. Unplug the machine first, then take the back panels off the first one is in the shape of a moon boot then the strengthening bar then the small half moon shaped panel.
The thermostat which may have gone is the one with the coloured dot. unplug the wires and undo the screw and remove it, only hold it by the terminals you have just taken the wires off.
Their is a small flat disk on the front, if this looks concave the thermostat has tripped, if you have a multimeter place it across the terminals no reading also means the thermostat is shot.
You can either by a new pair of stats, or you can try the following which has worked for me many times.
hold the thermostat approx 12 inches above a hard surface, this sounds harsh but you have nothing to lose. throw it as hard as you can at the floor. If the disk now looks convex (even slightly Convex) you have reset the terminals. Refit to dryer, re-assemble panels, turn timer to 20mins or more leave for two minutes open door if dryer is warm internally you have your fix, which is a dam sight cheaper than an £89 call out plus £20 for parts.
Hope this helps.-
Pixiemoon, December 2006