My white knight tumble dryer wont start

If the drum is not turning then i would say the Belt has come off the rear of the drum and needs to be checked firstly.
If there is a fault code then it could be the thermostat has tripped out its safety trip and needs to be reset.

Nothing works or drum fails to turn (tumble dryers)
Ensure that the power supply to the dryer is switched on, the timer is set to the desired drying time and the door is correctly closed. If you have a condenser model, also check that the bottle is empty and is fully pushed into the machine.
http://www.whiteknightrange.co.uk/whiteknight/faq.html

The first thing to establish when troubleshooting the clothes dryer is whether the dryer will start or not. If it won't, start by checking the outlet and the circuit breaker. Is the dryer plugged in or has it tripped the circuit breaker? If the breaker has been tripped, flip it back on and try the dryer again. The drum should turn without a problem.
If both plug and breaker are fine, you'll need to inspect the door switch as you continue to troubleshoot the tumble dryer. When you close the door on the dryer, a plastic peg should click and operate the switch which allows the dryer to work. The peg might be bent or broken, in which case it won't connect with the switch. You can try to straighten the peg, but if it's broken, you'll need to replace it. If the peg is fine, the switch has probably failed and will need to be replaced.
http://www.doityourself.com/stry/troubleshooting-a-clothes-dryer-drum-doesnt-tumble#b#ixzz3FOOQgtAT

Good luck!