It sounds as if you have checked the obvious. When you switch on the ignition, does the fuel pump prime, or run continuously? If it runs continuously, then you may have an ECU problem which will also affect your spark.
Have you tried removing a spark plug, plugging it into a lead then, whilst holding it against the engine block, looking for a spark whilst someone is turning the engine on the key? (Make sure you get a good earth, because you could damage the ECU otherwise, unless of course, the ECU has gone anyway.)
Is the dizzy the type that has an earth lead attached to it? If so, check that the earth lead is still attached. That will prevent it from starting.