Sedge8

Hi I have a 125 quat I just picked up, was running but fuel filter was leaking so I swapped it for a new one, pretty sure its the right way round as arrow points away from the tank, tried to start off a power pack as new battery has not arrived yet but it wouldn't start and at one point made a loudish bang, think it was a back fire from exhaust, tried to jump it off my car this morning and I could hear the starter wiring but only seemed to try to turn the engine momentarily every now and then, now it don't seem to turn the engine and have any sign of compression :/ please can somebody help with this as I'm new to motorbikes and have no idea