1998 318is Fan Blowing but No Air coming into Cockpit

Hi Guys,
I driver 318is 1998 E36, I can hear the sound of the Fan Blower Blowing very strongly but no air is coming into the Cockpit, what could be the problem ? Thanks
I driver 318is 1998 E36, I can hear the sound of the Fan Blower Blowing very strongly but no air is coming into the Cockpit, what could be the problem ? Thanks