Old but not much used Bosch fills up then does nothing!?

We have just been given our first dishwasher, an old Bosch Classix SG543A52GB/35 (number on top of inside door)... its been plumbed in... when the program button is pushed, the machine fills with water for approx 1 minute, then does nothing except make a few quiet clicks... we've taken the left hand side of the machine off to reveal the network of pipes etc... don't know what to do next! We did the laying it on its side thing & some water came out on to the floor but that didnt resolve it...