Kenjo is right.
Pull the machine out and tip it backward about 45 degrees.
Water will drip from the back of the machine (put some towels here to collect it).
Then reconnect the machine. It should start operating. If the drain pump starts running all the time again after some time, you've a leak and you should find it in the machine.
If tilting the machine has not resolved the issue, either the anti-flood float switch is stuck up or you have a different failure.
Try pouring some water into the machine, if you have the anti-flood system activated it will drain the water out. If it starts washing, you have another fault with water level sensors etc.
A.R.S., January 2013