So which version of OS is the unit running currently? What do you see on the console now? Do you have a support contract for the unit?
If not, when was the last time the unit did have support? Once you get the unit booting, you can reactivate the license and view the service check date. It must be later than the release date of the OS version you're wanting to install. See SOL7277 for details on this:
SOL7727: A service check date that is earlier than the license check date now requires you to relicense the system before upgrading
https://support.f5.com/kb/en-us/solutions/public/7000/700/sol7727.html
Aaron