if you could please fill out your sig so we can help you better. its tough to give suggestions when we dont know what model, year or trim level your car is.
on some newer cars the bcm is part of the security system and if you can wiggle wires and change your symptoms that might also not allow crank. if your bcm itself is bad you have to have the new one programed by the dealer.
i would try unplugging it and checking for loose wires on the connector and corrosion, try plugging it in and taking it out a couple times
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock