Help: Isolating UT Issues

Yesterday, we've decided to upgrade our Untangle PC. However upon isolating the UT machine from our network, and apply the modem >> router >> switch setup, client PCs experienced intermittent internet connection.

Previously UT was configured at 192.168.5.1, upon isolation, i reconfigured our router to 192.168.5.1 to temporarily service our LANs. Then the problem arises.

Any quick fix advice?

Thanks,