|Are the numbers five digits like: 41357|
If so, then it's possible those are DATES,
Excel stores dates as a number representing the number of days since 1900-Jan-0
Try reformatting the numbers and see what you get.
As for the X's, are they X's or Hash Marks: ###
If Hash marks, it just means the cell is to small to display the date,
if there X's then I have no idea.