Excel 200 Not Sorting Properly

When I sort a numbered list formatted as 'general' some of the numbers appear out of order. When I use the AutoFilter function the drop down list sorts the numbers is this weird fashion also. I reformated to 'number' and the same occurs. There does not appear to be a pattern to how it does this, because for example number 150 is listed several times; some will appear in the correct order and others will not. Retyping the data in the cell did not correct the problem. My spreadsheet is in Excel 2000. It has 24 columns with 700 records. A few blanks exist in the field I am trying to sort. Mis-sorted numbers do not appear immediately before or after the blanks. How do I correct this?