I have a 2008 Chevy Cobalt and the car won't start. I put the key in the ignition and it won't move.?

I already towed it to the dealer once regarding this and the first service guy got in the car and put the key in and it wouldn't move so he agreed. Then another technician got in the car a couple of hours later and the car started right up! They put some lubricant in the ignition where you put the key and said maybe that was it but weren't sure. Now it is happening again. Also, when it happens, the security light comes on the dash...is this related? Is this a security feature? Please help - thanks!