3 flashes from the end light is an anti flood error code. Water will have leaked into the base of the dishwasher and has activated the flood switch. That is why the pump is running all the time.
What you need to do is either pull the dishwasher out and tip it backwards and this will allow the water to drain out form the bottom so you may need a towel for that.
Or of its built in you can remove the wooden kickboard at the bottom of the kitchen and from there remove the metal panel beneath the door.
From there you can use a sponge or cloth to soak the water from the base but just make sure its unplugged.
Once its clear of water retry the dishwasher and see how it goes. But if it happens again then theres a water leak in there which you need to find and fix to cure this.
But the error code you have on there is a water leak in the base. If you need anymore info just get back to me.