There are a couple of scenarios:
Is she cranking over but not firing:
Most common here is voltage drop caused by bad connections on the high current cables (battery and starter motor) and/or battery itself.
I would replace/make up new ones as corrosion inside the crimped part cannot be seen. Have you tried turning her over without the plugs? This will give an indication of the health of the starter motor and associated cables and battery if she spins easily and quite quickly.
Not so common but also a known issue is the ignition switch.
If all this checks out, then it becomes a little more difficult as you now have to start checking the ignition system. A bit hard if you don't have other items to swap out (coils etc)
Is she not cranking but idiot lights come on and fuel pump primes when turning on ignition:
Check safety switches (clutch, neutral, fall) I know on my Classic, if I pull the clutch all the way in she won't turn over and I have to release the clutch a little before she'll turn over
Again, here there could also be an ignition/kill switch issue
Hope this helps..
