Sounds like the pump needs replacing or perhaps just the brushes in the pump. It might just be a blockage in the pump. You have not given much info about the model number. If it is 30 years old I'm suprised it hasn't stopped working before.
The fact that you have asked such a vague question makes me think you won't have sufficient knowledge but I guess everyone has to start somewhere.
Turn off at mains, remove access panel to give access to pump. If the pump has its own motor then that may be the problem. If the pump is driven off the same belt mechanism as the main cylinder then it is probably a blockage.
You may have trouble getting spares for something that old.
Be careful operating it with the covers off. If in doubt call an expert.
Ian Pedder
October 2006