engine turns over to start then locks up

96 4.3 blazer vin w edi ignition intake gasket was blown and then repaired. motor turns over without coil wire connected okay. but when connected it locks upon firing???????????? timing is set no.1 piston top dead center compression stroke.. timing marks on vibration damper aline with V mark on front of timing case cover top and timing mark on bottem of cover. distributor rotor points directly at No.6 mark on distributor body indcating No.1 spark plug firing position. Questions i have also is what is the reason for the alining the indent hole on the driven gear on the distributor shaft and the paint mark on the distributor housing??? can the distributor be placed in pointing proper but still be out acording to the cam sensor??? also i cant clear the codes on cumputer by disconnecting battery cables is there another way to clear codes?????? thanks to anyone can help me :banghead: :banghead: :banghead: :banghead:

Recheck the sparkplug wiring, sounds like a pair are crossed.

It takes a scan tool to reset the computer.