Block a cell depending on the sum of other cells

[Guest]

Hi,
I want to be able to block a cell if the sum of other cells are <0
Example:

If Sum(A1:A5)<0 then block A6

 

[Guest]

Select the cell, then
Look at Data=>Validation, select the custom option and put in your formula.
for additional information on using data validation, see

Debra Dalgleish
http://www.contextures.com/tiptech.html

look in the index for data validation.