I only say this because its not an intuitive design, but did you inadvertently turn it off by lowering the fan speed? I think if you do, the only way to power it back on is to push the fan speed increase button. Just a shot in the dark.
2012 X5: BSM/Black/Sport Activity/STi-R+
(Sold) 2013 BMW M3: JZB/Black/ZCP/M-DCT
(Sold) 2010 Audi S4: Deep Sea Blue/Black/Prestige/S-Tronic
(Sold) 2006 BMW 330i/Jet Black/Black
(Sold) 2005 Audi S4/Moro Blue/Black