318 Wont Start!

ok the other day i was working on my car (74 duster 318)cause it seemed like it had a lag or something in it and when it idle its was horable. so i replaced the spark plug wires the spark plugs and the cap and the rotor ran good for about a week and started doing the same thing it felt like i was driving a tank cause it was really really slow i had it floored and it wasnt going anywhere. so now i went to go look at it and the distriputor cap wasnt on all the way so i tryed to put it on i could hook one side but not the other. i made sure there were no wires going into it but it was on the way it was suppose to but still nothing its not getting any spark because it will try to turn over but nothing.... and if it sounds like i dont know what im doing it is because i dont this is my first mopar but im a fast learner...
thanks
Jeff duster