02 chevy impala ls

I did a gasket replacement from the block up and after reassembling everything and hooking all the connections up and what not went to start it and there is nothing at all. No interior lights no clicking no nothing. Tested the battery and its pumping 12.7 volts so non issue with the charge of the battery. The connections seem fine and everything’s hooked up. The original reason for gasket replacement was because I blew the upper intake manifold apart with a backfire and had to clean any and all particals of plastic out of the engine block. What would cause the starter to not get the juice? And no lights on dash or interior?