Spencer25,
If you have taken data from another source and added it to your sheet to be used in a lookup, you can get this behavior. It's caused by the laying on of data on top of a format. The data doesn't necessarily have the same format as the cell underneath. What happens when you change from text (adding ' ) and then back is what needs to happen to all the data. That is hit F2 and then Enter. That gets the data into the cell in the format of the underlying cell. To do this for a lot of data, you want a shortcut. You want to copy a blank cell and Paste Special, Add to the entire range of data. This will add zero to all the cells in much the same way as hitting F2 and then Enter.
Dufus