Firepower wont connect to ISP

[SeanDoody33996]

Hello! I am a System Admin and i'm trying to set up a new network for our new office and when trying to setup the 1120 firepower it doesn't want to connect to the ISP, I've watched a few videos on setup and for them it just seems to work and i'm not sure what i'm doing wrong for it to not connect. We had old equipment set up to use until the Cisco stuff came in and it worked just fine. the only thing that is changing the is router. It used to be a ubiquity router now its the firepower. Any help is appreciated. 

[balaji.bandi]

I follow the same Guide as below :

https://www.cisco.com/c/en/us/td/docs/security/firepower/quick_start/fp1010/firepower-1010-gsg/ftd-fdm.html

here are my questions to understand better about the environment.

you replacing another router with the same IP address configured on FTD?

if this is connecting to Switch - clear the arp - default some time take 3hours arp expiry depends on the setup.

give some high-level information, what devices in the network involved between user to the internet.

example :

user ----switch---FTD----Router---Internet ?