Can i Delete anti theft

I have been unable to start my 2000 Sable regularly for months, had it in 3 shops. I will put key in and turn to on only to have THEFT light flashing. It may be something simple for you, but it ain’t for me. If you have a second key, try it, or try disconnecting your battery for a few hours. But I have been told it is likely computer. And that is not good news $$$$$$$$$$$$