eftw5026

ok here is my delema, i have a 1999 c5. i took the car for a long ride when i parked it and then went to start it about an hour later, all i got was some dash lights. no cranking. so i thought the battery was no good. i put in a new battery and the car started no problem. then when i went to leave i put the key in and nothing. i figured out the only way i can start the car is by disconnecting and reconnecting the battery. that was 4 years ago. i was told its a bcm problem. so 2 months ago i sent out the bcm for repair and was told it was ok. it cost me 120.00 dollars. then a tech expert told me it was the ignition switch. so i replaced that with a new one. and nothing still the same problem. i also checked the resistance of the key pellet and the small wires that come out of the switch, both the same. i figured out that after i start the car and shut it off. it will start no problem up to about 15 minutes. after about 20 min or so, thats when it wont crank..im lost, can you help. i also just learned my steering lock doesnt work i dont know if this has anything to do with it...........