'98 cavalier aftermarket stereo

I am in the middle of installing an aftermarket sony xplod stereo in my 1998 chev cavalier. I used the wiring harness supplied with the stereo and hooked it up. Now the theft system light is turned on and the stereo will not turn on. I can tell that it is getting power because i canhear it power up when i turn on the car. If anyone has any ideas on how to solve my problem please let me know.

Thanks.

What do you hear when you turn the car on?  Have you used a volt meter to make sure you have 12 volts on the radio's red and yellow wires?

I would recomend that you disconnect all your wiring and rescheck what circuits you have connected to. It sounds like you have made a mistake. This is the prime reason you should have bought the correct plug for your car and wired it to your stereo's plug. It makes for a cleaner install and allows you to get the wiring right. You need to verify using a volt/ohms meter what each wire is for. Check for blown fuses in both fuse boxes. If you are lucky, nothing will be damaged.sparky