Can you steal a battery out of one of your other vehicles to test? I'm skeptical that the starter is dead.

I would suggest doing a leakdown test on the engine. If you blow bubbles in the coolant, that'll tell you a lot.

After that, check for spark and fuel.

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2011 M3
2006 Sierra 2500HD 4WD LBZ/Allison
2004 X5 3.0i 6MT
1995 M3 S50B32
1990 325is
1989 M3 S54B32

Hers:
1989 325iX
1996 911 Turbo