While driving the 2000 X5 today after not driving it for a couple of weeks, in the 20* weather, the low coolant light came on, then smoke started pouring out. As I was pulling in to the closest lot about 1/10th of a mile away, the trans failsafe lit up and the trans was slipping. The coolant was completely empty.

Any suggestions on what I'm looking at before taking it in to the shop?

Thanks!