Ignition

I have a 1999 chevy express van. I bagan having problems to start the engine. I would let it sit for 10 to 15 minuits and it would start again. And that's been going on for some time, but 2 days ago it just didnt start for days and the security light was blinking. I checked the fuel pump pressure it is good, the coil, it has new roter and cap, wires, filter, every thing is working perfect. So I started playing with the ignition lock and it started again. I noticed that the key cilinder is kind of loose. Could it be that the problem is on the lock switch or the ignition switch, and how can I know