Hey Ashley, Sometimes Norton antivirus installation gets failed that's why get this Error Message.
Don't worry i will help you with this installation problem.
To Fix this Norton Error 8504:
- uninstall the Old Norton Security from your Laptop Using the Norton removal tool.

- After removing Norton Antivirus please Restart Your Laptop
- Now verify your Norton Version and Setup Norton again.
Setup Norton Antivirus Security-
If you have a Norton product key then you can use your 25 alpha numeric digits product key and download the installation file by visiting
norton.com/setup, on this website you will be get an option to enter your product key. After entering the product key the setup file will downloaded, double click on this file to install the latest version of
Norton in your Laptop.
Thanks & regards
Alisha