First of all, you should not use fake or incorrect keys. You have to be sure about the product key. It should be valid so you can install Excel, Outlook, PowerPoint, and others. If you haven't a valid key, then the installation will fail.
On the other hand, If you are using a trial version of the MS office, the software will provide you with use for a certain period. When the period is over, you have to verify the MS office. Otherwise, Ms. Office will stop working on your system.
That's why; you have to verify the product key either after installing or over the trial period.