Help me you're my only hope

Hello all

I've been sent to a office site which has been having on and off phone issues for a while. I've found that when the phone system is connected to the network, all phones stop working. When the ethernet cable connecting to the LAN is pulled out, the phone system starts working again.

Theres a handful of IP phones not working either, theres 3 that are plugged into the phone switch directly works. But reset when the phone switch connects to the LAN

I can't find any network loops, theres no VLANS or any fancy networking settings. Just can't figure out the issue, any ideas?

If this sub doesn't allow help me posts, please remove.

Thanks,