Oil leak and engine stalled

[Perrier]

2004 X5 3.0

Driving in cold weather (-10c) and car was driving normal but with a clear smell of burning oil. Got off the highway and car stalled at the traffic light. Check Engine light came on and engine will not turn. Checked under hood and there is oil around the (alternator?) on the front passenger side of the engine.
Checked oil level, very low, filled 3quarts. Engine still will not turn. I checked oil level 4 days ago and it was within limit on the dipstick. Oil light did not turn on.

Any suggestions on where to start, or anyone with similar experience?

By the way, towed the car to dealer only to find out there lot gate was closed and had to tow it home. I don't understand why would they have a drop box for the keys if I can't leave the car, but that's another story.