not starting after replacing transmission sounds like something is preventing the engine from turning over

Replaced entire transmission, hooked everything back up, reset mongoose alarm system with supplied code, dash lights up no unusual lights, like no check engine light turns off like usual. I got a mate to walk starter motor with a hammer as turned key can hear it working but not turning almost sounds as if something is stopping it from turning engine over, also when trying to start can hear a whirring sound coming from the fuse box area inside engine compartment. Help please!