How can I fix my Hoover Elite II VACUUM? The bag isn't inflating?

It turns on, brush turns quickly, but the bag doesn't inflate and the hair & dirt seem to come out of the bottom instead of going into the bag. The bag is on correctly & tight, and I just changed it. I did run over a rock the size of a quarter right before this though...wonder if that did something. The rock went into the old bag, so I know what happened to it. What do you think is wrong with it, and do you think I can fix this? Thanks in advance!