Truck wont start

[85chevylwb]

OK, so i got into my truck this morning to go to work and when i put the key in the ignition, it turns like normal but nothing happens, almost like the kep is free spinning with not resitance like normal to start the truck, im wondering if its the lock cylinder or the ignition switch, im leaning towards the lock cyclinder but not 100% sure. either way, can anyone tell me how difficult it is to replace either one. this is my daily driver and need to get this fixed asap. thank you for your help in advance.