Help with my piaggio zip 50cc not starting???

Ok, need a bit of help if possible?
I have a piaggio zip 50cc which was running fine until a few weeks back, started once, then died, and I havent been able to start it since. Since this has happened ive changed the spark plug 3 times , charged the battery fully more than once, bought a new inlet manifold as the old one was torn badly, bought a new k&N air filter..but still no luck..
The only thing is that My bike dosent have a kickstart as it had to be removed after it broke on me whilst out riding.
So any help would be appreciated asap as im looking at selling it soon?

thanks