1998 grand prix gt wont randomly wont start!!

Im new with cars but am learning rather quickly because my car keeps screwing me. Someday my GP will decide not to start then i cant get my key out (figured how to remove it thogh). The engine wont turn over, no internal lights (ex. dashboard, glove box) no external lights, no signs of life at all. Then i will come back in about a half hour, and it will start like nothing is wrong. Ive had the battery tested, the altenator, and the starter, and they all tested out fine. I cant afford to have a mechanic fix things that dont need to be, so if anyone has any tips, Im all ears

P.S.

Im new here so I apologize if I posted in the wrong spot

When you turn the key to the point right before you would start it do you have power and then it goes dead, or you just have no juice at all at any time?

Check your battery cables for corrosion, and check all the grounds to be sure they are clean and tight. These cars are picky about this. One time I had my neg. cable corrode just a bit and was also vibrated slightly loose and as soon as I hit the key to start it the entire car went dead. Cleaned cable and retightened and no issue since.

Sounds like it could be the ignition switch.