1975 Chevy Monte Carlo engine not firing

Is it cranking over and won't start or just won't crank at all ? Please! explain

The engine turns over but it just won't fire or start. Last year i took off my stock exaust manifolds and put on racing headers in order for me to get my new headers on i had to unhook the plug wires and take out the spark plugs. After i put on my new headers i also put in new spark plugs. I did hook up the plug wires in the right firing order. But when tried to crank the engine it would only turn over so i tested it to see if it was firing and it was not. By the way the engine has an HEI distributor.

Disconnect a sparkplug wire or 2 and ground it to the engine -have helper crank engine over-do you have a snapping blue spark? No snapping blue spark continue to troubleshoot the ignition system-power input to the coil/coil packs,distributor pick-up coil, ignition control module, cam and crank sensors- Note: If it doesn't apply disregard it