HELP!

I am borrowing my mom's 2003 Chevy Trail blazer and it has 83,000 miles on it, i am not sure of the engine size but i need your help! I was coming out of a grocery store and i went to start the car and the key would not turn- i tried turning the wheel, made sure it was in park, made sure all the doors and trunk were shut and locked, and after waiting for a half hour, i tried again. i searched for a button to turn of the security system(i don't know if that has anything to do with the issue or not)- but there wasn't one- so i tried yet again to turn the car on again and it wouldn't budge! I don't know what to do- please help me!
~Katie