Hope you can help me!

I am working on a 1993 Blazer 4X4 with a 4.3l, V-6,CPI. I replaced both intake gaskets and valve cover gaskets, also the starter. The problem is that now I can't get the thing to start. I've looked the whole thing over and can't see any missing parts or disconnected wires. I have spark and fuel. It sounds like it wants to start but just won't do it. There is smoke comming out of the exhaust while it is being cranked over. I have done this many, many times in the past and have never experienced this before. Maybe the computer, I don't know. I've also sure that the timing is right. No. 1 piston up in the compression stroke and the rotor pointing at no. 1 spark plug.:(