Should keep it to your original thread...
A mod will likely close the other thread soon...
Anyway..
1. Make sure you're formatting the cell as general or number
PRIOR TO entering the number. Formatting a cell AFTER entering the number will not change the value in the cell.
2. Do you have any VBA code in the book? - Disable macros and save/reopen the book to test. Does the problem still occur?
3. Does it occur in ALL books/sheets? Or just one in particular?
4. Does the # appear in the Cell, or the Formula bar, or both?
5. Is this related to this thread?
http://www.mrexcel.com/forum/showthread.php?t=531143
Are you entering the number in one cell, but it's actually a different cell with a formula that is giving you this problem?