My kenmore vacuum 116.31913 is blowing air out, which blows dust etc. away from the vacuum. The vacuum is not pulling dirt in.

I had put a clean bag in it, which was securely attached, but animal fur, etc. had balled up and not gone in the bag. The dirt was minimal, I vacuum very regularly and often. I cleaned everything up, and when I tried it again, the same thing happened.
How can I fix this?

Gail, April 2011