Radio and all windows quit working.

I have a 1999 Pontiac Grand Prix and sometime back my ignition key became troublesome. I have to use a screwdriver in the release slot to remove the key. About the same time my shifter would shift from park without depressing the interlock button. Now my remote won't lock/unlock. I replaced battery, nothing. I checked my fuses (inside glove box, and under hood) and now my radio quit ( theft light flashes) and all the windows won't work. I can't reprogram because the key won't go into ACC. I tried to use my code on the radio but it will display the time. HELP!

Since the fuses appear to be good have you checked at key fuses to see if there is 12v physically present? It sounds the body control module (BCM) and other components are missing various feeds of 12v from the battery and ignition switch. For example if you check for 12v at the MALL PGM, BTSI, MALL, PWR DRLK, etc. If the 12v is missing then you'll need to back track to the ignition switch. If present then forward to the BCM.

The reason why the power windows are not working is because the 12v is missing at the Power Window Circuit Breaker. The Retained Accessory Power (RAP) relay feeds 12v to the circuit breaker and is energized by the BCM.

I'd suspect the ignition switch and harness assembly first and the body control module second.

Try cleaning all the battery cables and have the car battery checked. Low battery voltage/bad connections can cause all kinds of electrical gremlins.