When a formula refuses to calculate, changing random pieces usually makes diagnosis slower. A consistent debugging order helps separate text problems from workbook problems.
Check the formula shell first
Confirm the leading equals sign, balanced parentheses and closed text strings. These are mechanical checks that do not require workbook context.
Look at separators and locale
A formula copied from another region may use commas where the receiving installation expects semicolons. Function language can also differ.
Inspect functions and names
An unfamiliar token followed by parentheses may be a misspelled function, a newer function, an add-in function or a localized name. Do not automatically replace it until you know which case applies.
Test references and criteria last
Once syntax is clean, verify that ranges exist, criteria point to the intended cells and text or numeric data types match the calculation.