Locking cell if sum of other cells is 0

[Elfego Baca]

I would like cells G5,H5,I5, J5, K5, L5, M5, and N5 to be locked until
the sum of E5+F5 is greater than 0. I would like to do this for all rows
in the worksheet.

 

[Joerg]

In this case you could use conditional formatting:
Go to cell G5
From the menu choose Data => Validation
Validation criteria:Custom
"Ignore blank" checkbox: Unchecked (!)
Formula: =($E5+$F5)>0

Choose the "Error alert" tab and into Title field put something like "Input
restricted", into Error message field something like "The total of column E
and F must be > 0 before you can input data here!"

Push OK

Now G5 is "locked" (no input possible) unless the sum of E5+F5 is greater
than 0.
Copy G5 up to N5 and down as may rows as needed.

Cheers

Joerg Mochikun