Adding onto what Thierry said, if you cant use PrtSc or any of the f1, f2, f3 or any of the f keys, hold down (Fn) while pressing any of the f keys or keys with two meanings. It should be next to the Windows key, which is next to Alt, which is next to the spacebar on the bottom row. It may not be in that location, but it's still on the bottom row. Saying this just in case you cant use PrtSc or any of the f keys... Learned from experience xD