How can I start my JCB Loadall 520-2 Year 1982?

The machine is a JCB Loadall 520-2 Year 1982.
The machine has just recently refused to start. Before, she was starting on the button without any hesitation. Then the pull stop mechanism stopped working and I had to manually operate the fuel cut off lever in the engine compartment. I did this maybe once or twice to start and stop the machine and then the next day when I try to start it, it won't start. There is plenty of fuel, the engine is turning over on a new battery but it is not even smoking. I'm frustrated because I'm sure that it is something fairly simple, probably something that I've unwittingly disturbed when manually operating the fuel cut off but can't work out what it is. Can any one help because it is hard lifting blocks up a scaffold without it!