It could mean a couple of things.

1. The columnwidth is too narrow to show the number.
2. You have a date/time in that cell and it's negative
3. You have a lot of text in the cell, the cell is formatted as Text.

To fix #1: Widen the column or change the font size of that cell
To fix #2: Don't use negative dates.
Don't use negative times/dates. But if you have to, change
Tools|options|Calculation Tab|and check 1904 date system
(but this can cause trouble--watch what happens to your dates
and watch what happens when you copy|paste dates to a different
workbook that doesn't use this setting
To fix #3: Format the cell as general.

Hawc911 Productions wrote:

I'll put in a formula in a cell and sometimes it works fine with not trouble.
Then other times it shows ####### right off and still other times it shows
it only after you've used the same formula a few times. What does the
####### mean?

--

Dave Peterson