Get your manual for your GXH50 and find the section for the low oil shut off . It is an external circuit on the outside of the motor, located on the bottom of the motor. If when you had your bike at a 90 degree angle some of the engine oil may have drained out along with the oil from your gearbox. If so then the low oil circuit will not let the GXH50 run. Its all in the engine / motor manual. There should be instructions in there that shows how to by pass this circuit for testing. Hope this helps,
Papa