Hi Nicholas,Try from another PC, or even from your mobile phone. As the admin console is just a web page, you can connect from a browser on your phone.
You will need to do a bit of testing. This doesnt seem to be a PBX issue but a network issue that you will need to troubleshoot.
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.