imported an existing database - need to change and delete categories


I've imported an existing client database. It has about 40 categories. First, I simply deleted them all but when I go to my Posts or Pages, nothing shows up! Most of the content (pages) is still showing up on the frontend but not the backend. It still says I have (342) posts or whatever but they don't show up.

I tried deleting all the categories except the "Uncategorized" with 89 posts in it but even then on the backend 89 posts do not appear.

Do I need to do some remapping in the database to make this happen? This seems odd that categories would connect anything.