Put aftermarket radio in 2001 venture now the security system will not allow the vehicle to start what can I do to fix it

What is your question?

I put an aftermarket radio in my 2001 Chevy Venture now the security light comes on and flashes and will not let the car start it will not crank or anything I unplugged the system to reset and it still does the same thing what can I do to fix it

What makes this problem better or worse?

Nothing the car already does nothing except for security light flashes

How long has your 2001 Chevrolet Venture had this problem?

The problem started when I put an aftermarket radio in the car and it has not worked since