Any stored codes?
You may need to reboot. There have been a few reported instances where the battery slowly died, and the car would not start after the battery was recharged. Unfortunately, the owners selfishly never reported back as to how they solved the problem.
I suggest a reboot. One or more modules may have suffered from a slowly dying battery. Open the trunk, wait 16 min until the trunk lights go out, and disconnect the negative lead of the battery where it's connected to the chassis. Wait 10 min or so, and reconnect.
Solve the problem? Report back.
Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.