It sounds like a weak or dead battery. Try charging it over night and see if it will hold a charge. Or you can jump start it and take it in for a battery check at a local service station. If your battery is a few years old it is probably the culprit. You can remove the battery and take it into an AutoZone or similar store and they will usually test it for free.

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'06 X5 4.8is, TiAg/black, cold weather pkg., comfort seats
'07 750Li, TiAg/black, sport pkg.
'05 Ford F350 silver met./slate gray, Lariat, 6.0 PSD, CC, DRW, FX4