IMac Killing network port

Question

This involves a iMac G3 500 mhz, running 10.3.9.
First I have to say I am know next to nothing about networking, I'll try to explain what is going on and am looking for whatever info any one can offer me as to why this problem may be happening.
Problem: Every morning the iMac when started up cannot find the network in our office. The port is completely dead, under system prefs, under network status it is completely blank not even a red circle saying built in ethernet is there but no connection.
I think it's the line (we recently moved to a new office) and someone else thinks it's the mac killing the port. When I connect another machine (also iMac) onto that port it also can't find the port and does the same thing. I've been told that's because the first mac has already killed the port and hooking anything else up will not work either.
I moved the problem machine to a different network port this a.m. and it works. The someone else is freaked out that tomorrow when the mac starts up that it will now kill this port too. He says it's already killed 9 ports on the switch/hub (correct term?) and he can't get them back active.
In our old office this never was a problem. I've been told that's because the old switch/hub was a non secure switch so it let the mac do whatever it wanted and that it gave itself a static ip address. Now we have a secure switch and it's not letting the mac do what it wants and is not regonizing this ip address. I've also been told that the machine probably has adware/spyware and that is why it's killing the network port it's connected to.
I guess I'm wondering - is it possible for a mac to kill a network port? Is it possible that adware/spyware is making the mac kill the port? If it is killing ports then why didn't it when it was moved to the new port this a.m.?
We have 8 mac in the office and none of them have this same problem. I can't imagine that out of 9 macs only 1 would have adware/spyware.
Thanks for any help

Answer 1

So before, you were using a hub with no routing capabilities, and "port-killer" was getting a self-assigned "169.x.x.x" IP address? Is this how the other Macs were doing it?
How is your System Preferences Networking stuff configured? DHCP? Or static with defined network mask and DNS servers? Built-in Ethernet, right? Is this the same as all the other Macs on your network?
It could be a hardware problem with either the Mac or the new router or its cabling. Here is how I would proceed to troubleshoot:
The first thing I'd do is reboot your router with a known good Mac plugged in to the dead port, and "port-killer" plugged into a known good port then boot up both Macs and see how they behave. If "port-killer" is truly living up to his legacy, you guys need to get a new router anyways, so what's another dead port?
If you now have two apparently dead ports then replace "port-killer" with a third known good computer. If both ports on the router are still dead now, then "port killer" is living up to his name and both it and the router need to be fixed. By the way, I would also do cold-boots with computers and router every time I made a configuration change in this procedure.
If "port-killer" is the only dead computer on the network and the other one works in the previously suspect port, then the router is okay and only "port-killer" needs to be fixed.
If "port killer" is working okay on his new jack, and the original "problem child" port on the router is still dead, it could be the router or it could be the cabling between router and computer. To determine which, unplug the cables on the "dead" port and a known good port at the router. Cross them and plug them back in. The good line now goes to the (previously) dead jack at the "bad" computer location and the (possibly) bad line goes to the previously good computer location.
Who's broke now? Same computer? Then it's in the cabling. Different computer? That router port is flakey.
The fact that you have already connected another Mac onto the "problem child" line and it's DOA, and that "port-killer" works okay plugged in elsewhere tells me that it's a router port or cable issue. Most likely the stupid cable is not plugged in at the router at all, and/or is mislabeled and running off to a different unused jack in your new office location.