how can i fix it?

i brought my midi moto and it was working fine. got it home and the key start does not wark any more. i raised the back wheel off the floor and started the bike with the pull start, i have a few problems one being the pull cord does not wind back in after getting it started. also when the bike is on, i put revs in it but if i lower the wheel to the floor it cuts out .. any ideas why ?