The logic that Terry gives needs a correction, or it risks allowing the OP's problem to repeat itself.
The OP's confirmed problem (see comments on question) was that there was an IP address conflict, due to the fact that the firewall and router both had the same, default, statically-assigned IP address. The solution was to manually change the static IP of the router, resolving the conflict.
However, the logic Terry expresses to underpin his answer is misleading, when he said that, "If the IP address of your router is not within the same range as your DHCP server, you will not be able to access it." In fact, you want your static IPs to be placed outside the range which the DHCP Server uses to lease IPs, in order to prevent future conflicts when a new device is connected via DHCP. The important mechanic at work (as Terry's example correctly denotes) is that all hosts share the same network range per the subnet mask.
For example, if your subnet mask is 255.255.255.0, and the rest of your network's IPs have as their first three numbers 192.168.1.x, then you could have x=1 be the gateway (the firewall in this case), 2<=x<=50 be reserved to be statically (manually) assigned (x=2 would make a good router IP), and have the DHCP pull from the range 51<=x<=100. All 192.168.1.x hosts can communicate with each other being on the same network/subnet, regardless of static/dynamic origination. But the DHCP will never step on the toes of your static addresses.
(Reference [see section How IP Address Conflicts Happen, second bullet]: https://www.lifewire.com/what-is-ip-address-conflict-818381 )