Formula Cells keep reformatting as text

[thejd99]

I got a file from a coworker that had the data formatted as a table. I went to the Design tab and selected "Covert to Range" to make it just a regular worksheet. When I tried to do a vlookup (or any calculation for that matter) I realized it's all formatted as text. So for the columns I wanted to do calculations I did Data-Text to Columns and formatted it as general, and I was then able to use formulas. However, every time I make a change to a formula it resets to text and I have to do the Data-Text to Columns trick again. How do I stop this from happening?