1997 Chevy Truck Hard to Start

Having trouble getting my truck to start. It cranks like crazy, but won't start. If I turn the key off and on a few times, sometimes that helps. Had it in the shop, they replaced the basic tune-up stuff (cap, rotor, plugs & wires) and it didn't help much. Once it starts, it runs fine. After they did the tune-up, the check engine light came on; they say that is the catalyic convertor, which I replaced a couple years ago. They're gong to warranty that, so it won't cost me anything, but I don't see how that relates to the starting problem. The fuel pump was replaced about 3 years ago.