Agree with greg about the switch and points. Also check the ballast, I had one that droped the voltage too much and I had no spark.
I had 12v going into the ballast and only around 5- 6 coming out, should be more like 9v. **** What engine do you have??? F, L head, or buick odd or even fire? If you have the odd fire it is very easy to get the wrong dist (even fire), and I think that would give no spark