It sounds like your table of values is formatted as text. Click on one of the values and check the format type. You can see this just under the word "Help" in the Home tab.
To convert all of the text-formatted numbers at once, type the number "1" in any cell that is a formatted as General or as a Number. Copy that "1" onto the clipboard; then select every cell that has the Text-formatted numbers, right-click on any one of them and select "Paste Special". In the small menu that pops out, select "Paste Special" again. In the next menu, under "Operation", select "Multiply" and "OK". MAX and MIN should now operate as expected.