Need help

[Redconvertible]

In need of help or ideas. I have an 89 RX7 convertible that I attempted to replace the factory radio in. Upon removing the radio from the dash and installing the aftermarket system I noticed the aftermarket system not functioning properly. I put the factory radio back in but now the car won't start. The battery is good and it starts to turn over but won't start. I thought it was flooded but have waited hours with no luck. My factory alarm won't set but if I unlock the car from the drivers side the security light flashes. Also when I remove the key from the ignition the security light flashes. Any help would be appreciated.