When converting numbers stored as strings (when they include a comma) into a number, your best bet is to first remove all non-number characters from the field before doing the conversion in the Select tool. Using the formula replace([start],',','') where "[start]" is the name of your original text field should do the trick.
You can also try to use ToNumber(Column Name) formula in the formula tool to convert string column into a new number column once get rid of string rows. In case you don't remove string rows, they will turn into 0.
