Check unit number against list

Hello,
I have a spreadsheet where I schedule units in for service. On the last sheet of the workbook I have linked it to a list of units that are NOT able to be booked for serivce.
As I am entering unit numbers in to be scheduled I would like excel to check the units I enter against said list and if one of the units is on the list have it turn red, or not be able to be entered, etc.
I think I need to use an IF Statment, and the MATCH function to compare my entry against the list, but I cant understand how to tie it all together and then apply conditional formatting.

Any help would be greatly appreciated.

Thanks.
Todd

Sounds like you could use conditional formatting with a lookup criterion for this. Can you attach a sample of your data (dummy data is fine)? If so, it's easier to provide exactly what you need.