I'm guessing that you're getting either an E2 or an E9 error code.
If so, open the door, switch it off, switch it on and immediately press the program button 4 times within 3 seconds. (Don't wait for any lights when you switch it on, just quickly press the button 4 times).
The two end lights should light up. Press the program button and one of the lights should go off.
Switch it off for about 20 seconds, switch it on, switch it off for about 20 seconds, switch it on and it should be reset.
If resetting doesn't cure it, check that the base isn't flooded and the anti flood device activated.
If you're getting any other error code don't do the reset, just post the lights that are flashing, 1 being left and 5 being right.