+1 on the cabin filter. I can't imagine the filters would be clogged bad enough to cause that kind of problem though...they'd have to REALLY be full of yuck for that to happen, and you'd probably smell it. Good place to at least start though.
It seems odd to me that you're not getting anything out of the vents though. Is there ANY air moving, or is it completely dead? If it's completely dead, it almost sounds like something is lodged just inside of the blower preventing the air from circulating. Strange. Let us know whats up if you get it figured out.