2001 Saturn L200 temperature problem

When my car is parked in the sun for a number of hours and the temperature inside rises to above 100 degrees. The car will turn over but will not start untill the car cools off. then it may start but the security light and most other warning lights stay lit up. But the car will not go into gear its like the computer has it locked up. Also the power locks will not work and the horn has gone off eraticly once. Also i tried disconnecting the battery to reset the computer and the mileage cleared the mileage went from 120,000 to 000,000. so it has to be some type of computer problem