Here is a way to check if a string is a number:-

public static bool isNumeric(string val, System.Globalization.NumberStyles NumberStyle)
    {
        Double result;
        return Double.TryParse(val, NumberStyle, System.Globalization.CultureInfo.CurrentCulture, out result);
    }

Here is a link so you can figure out what to put in the “NumberStyle” field.
http://msdn.microsoft.com/en-us/library/system.globalization.numberstyles.aspx