HanSewLow: The UI can be a little finicky in DAO. Typically, you need to drag the item to be "quick barred" into just the right spot in the square in order for it to slot correctly. If you're playing at a high resolution, this can sometimes be a little troublesome because the boxes are smaller. However, it should not be too difficult to do.
When you drag an item/ability to the quick bar, the square you have selected will brighten slightly when you've hit the right spot. At that point, release the mouse button to save the desired item to the bar. You can also rearrange quick bar slots this way as well.
To remove something from the quick bar, drag it somewhere else on the screen and release the mouse button.
I deleted my game and started a new one. Problem fixed. Must have been a glitch. Thanks for the reply!