Why wont your car start when it gets warm but it will when its cold?

Right off it sounds like a component gets too warm and fails, but works cold. Is the engine getting fuel when warm? Does it have spark when warm? Knowing the answers to those questions as well as make, model, year and engine size would help to answer your question.

I had a similar problem with a 1987 Chevy Celebrity. I replaced the ignition module and the crankshaft sensor and it runs fine now.