Car Will Only Start Periodically.

Hello Guys. Im new to the site but i could use some help. I have a 2001 Mustang Gt. It has a few upgrades. I recently installed a spec 3 clutch and the car was great. I am having a problem now with the car cranking. When i turn the ignition switch all the lights com on but no fire. I replaced the clutch switch thinking that was the problem. I can turn the switch back an forth and some times it will start. once its running it is fine. Do you think i have some sort of short in the wiring under the dash or could it be a bad ignition switch.. Thanks for any help you could give.

thanks squeak93 The theft light is fine. i finally fixed it after replacing the clutch switch, the ignition switch and the starter. It turned out to be a bad ground. I loosened all the grounds under the hood and retightened them all was good..