It could be either a mechanical problem with the clutch or an electrical control problem with the circuit board. Neither are easy to explain how to do on a site like this. Both involve the need for test equipment & a good basic knowledge of how it works. I would suggest you call in a service company to do it for you.
Lincoln Appliance NZ
July 2009
I can answer this question...
How can I fix my washing machine? It is a Simpson Aquapulse 513?