Car cranks but wants to start when i release the key but wont run

maybe you guys can help me with this headache. Right now i have a small block 408 1974 dart and i am having trouble with start up. I have an electronic ignition with the orange box and the msd blaster ss coil with a recurved stock distributor. I have already replaced the box, original coil, ballast resistor, and ignition switch in the column. I dont know what else could be causing this situation. Any suggestions will be a big help.
-Jake