Errors in simple sum function

[Dave]

I am somewhat confused by the errors in my spreadsheet. I am using excel 2007
I have a fairly extensive spreadsheet that in on section of the spread sheet
I am getting total fictitious results use the sum function or even using
=x+y+z in that same section (columns U through Y) adding 3,000 + 475 is
giving me 9,996,400,232 I am completely baffled I have used excel forever any
help out there

 

[David Biddulph]

U to Y is 5 columns. You talk of 3000 and 475, but do the other cells
contain numbers which are perhaps hidden with font colour set to background
colour or by some unusual custom formatting?
Does =COUNT(U2:Y2) give 2, or a larger number?
Which cells are your 2 visible numbers in? What happens if you just add
those 2 cells? What happens if you add the remaining cells in your range?
Have you looked at the formatting of the numbers for the cells in which your
numbers appear?