Excel Question - modified spread sheet differential

Help please - I have 2 spread sheets with lots of columns and about 1000 rows each. Some of the cells in each have changed.

I need to find which cells (or at least rows that contain those cells) have changed. Using duplicate removal i can see there are about 175 records what have changed.

I have tried a few ways to compare and had some success but i need to make sure i get every one.

Any suggestions?

use a third worksheet to highlight cells from the first two worksheets that are not the same?

e.g
get data of one spreadsheet on one worksheet (Sheet1) and data of other spreadsheet on another (Sheet2).

on the third worksheet apply formula to a1 cell
=IF(Sheet1!A1<>Sheet2!A1,Sheet1!A1,""

fill down and right to apply calculation on other cells

Its not easy to get them in the same order due to the changes (theres no unique id) but that gets me a fair way.