When I changed the CPU, the car will crank over but will not start. The key light indicator flashes while cranking over. What do I need to do?

First, check all under-hood and under-dash fuses, paying particular attention to the ACG (S) under-dash fuse, which controls power to main relay Terminal 5. If this fuse is missing or blown, main relay Terminal 8, which is the computer-controlled "grounding terminal", will not receive power and the car won't start. Use a multimeter or test light to test each fuse, otherwise you run the risk of replacing the fuse in the wrong slot. Second, tell me if you hear the main relay click and the fuel pump run, when you turn the ignition to ON. Third, check for any diagnostic trouble codes.

If you want me to help diagnose your car's problem, you need to respond much faster. It takes active participation by both parties; otherwise, it doesn't work.