Applying some display format does not change cell content or data type (which the ' leading apostrophe in the Input Line is an indicator for, text could be interpreted as numeric but is text). Convert data to numeric if you want to calculate with. See this FAQ EarnestAl already linked to.
Delete column K. It contains some white space.
Enter some column header into D1.
Click any cell in the Date column and then a sort button.
Click any cell in the Sym column and then a sort button.
Now it is sorted by Sym and Date with column headers detected automatically.