Network tripping - low connectivity

Hi guys,

Usually I can solve 99% of technical problems but this one has me completely stumped. Calling all networking gurus.

I have several devices including 3 desktop PC's wired into a modem/router. I have expanded the router to a 6 port switch. If a device requests the internet through the switch or wirelessly the entire network trips out and although the modem/router is showing "connected" through it's LEDs there is "limited or no connectivity" shown on all the desktop PC's.

I have tried exchanging the switch for a replacement and have also replaced all the patch cables linking the devices to the modem/router.

I have also replaced the modem/router with a different brand, but still experience the same problem.

This particularly becomes a problem if one of the xbox consoles connects through the switch, but the network crashes several times a day anyway.

I have upgraded the router (D-link) to the latest firmware, this has been running without fault for over 2 years. It's only been the last 2 months where I have experienced this incredibly annoying issue.

The temporary fix is to restart the modem/router and wait for the network to come back up. If the xbox console has tripped the network, it has to be left "ON" then I restart the connection to get any life. It does in the end fall over again.

I have tried assigning static LAN ips to the desktops, this has not made any difference.

As you can imagine this is driving me mad. Any help or advice would be so appreciated.

Thank you in advance.

So the problem first appeared with the addition of the switch? And you replaced the switch? What brand/model number?