Hey Conal, try these 2 simple things. First, go out and buy a new light bulb for your brake light. Put it in, then try to start it. Some mopeds will not start if the brake bulb is blown or damaged. (plus if this is the problem, its a $1.50 fix)
The second thing is make sure the breather hole on your gas cap is not clogged. This can cause the ped to run poorly or not at all.