Compare a List and Highlight Similarities

This looks for duplicate entries in 3 columns, comparing column A to the other two.

Go to Conditional Formatting, Manage Rules, Select Worksheet and you will see the 3 rules that accomplish this. Select a rule, click on EDIT and you will see the formula for the rule. If you want to edit the rule, click in the field and press F2 before typing in the field otherwise you will get a lot of characters in there that you don't want.

The current rules are only for 50 rows. You can increase this to what you will need. You will have to do this for all the rules. Then when you click ok, you will be taken back to the list of rules where there is a field called "Applies To". Click in the field on one of the entries, press F2 and edit the 50 to whatever you put in the formulae that you edited. Repeat for each of the rules. Click Apply.