Key is incorrect

I purchased a laptop about a month ago, and haven't been able to write the
correct product key. I have tryied so many times that the system already gave
me an error message.

When I write the product key, when promted by the office programs, I write
the product key that appears at the bottom of the laptop, and after it
automatically gives me the following messge: The key is incorrect. Verify
that you have the correct key, and then retype it.

I'm sure that the key that I'm typing is correct(bottom of laptop). Please
advice what to do!