Today, I experienced the same problem on my 2005 X5. The fan would not turn off, even with the key removed from the car. All lights not lit or functioning on control panel. Hot air coming out of the vents.

I disconnected all 4 cable bundles and then reconnected them and the control panel worked ok. After all of these years, there must have been a poor connection.

If your control panel still does not work, there are a couple of videos on YouTube on how to repair a capacitor on the controller board. To get a used unit, the cost on eBay is $200-$300. Some report brand new one is over $900 so if you are good at soldering electronic components then you can save some money by doing your own repair.