Plug PC into Airport/ it kills internet and jumps to 100% CPU usage

[pgaiduk]

I have a functioning network with a Mac Pro (primary box), Mac Mini, 3 Dells, 2 wireless IBM laptops and 2 wireless netbooks all connecting either wired or wirelessly through my Airport Extreme and an ethernet switch. Everything works well UNTIL I boot up and plug in my aging Gateway tower. It works fine and boots up nicely but when I plug it in to the network, it's cpu usage stat jumps immediately to 100% and it kills internet access for itself and to my other machines through the Airport even though the Airport's light is happily blinking green. Its been under my desk for a couple years but I'd like to retrieve the contents of it's hard drive via Fusion before I give it away.
I know its a Mac forum but maybe an Airport setting??
I'm desperate - I've already messed with it for a couple of days to no avail.
Any ideas?
Thanks

 

[sycho]

It's most likely spyware or something to that extent.

Reboot it in safemode and see if it does the same thing. Press F8 while booting and select "Safemode with network" and see what happens.

 

[Makosuke]

Well, I've seen exactly the symptom you're describing on an old (but not ancient) IBM tower, and in my case it shut down the network for an entire 48-port professional switch.

Unfortunately (for you) the cause was failed ethernet hardware, which may well be what you're seeing.

The other possibility I can think of is that there's a virus on the PC, and as soon as it sees a network it's going nuts trying to do whatever badness it does, pegging the processor and overloading the hub in the process. You could see what process is taking up 100% CPU, which might give a hint, though I would expect a situation like that to result in the hub just running slow, not dying entirely.

 

[pgaiduk]

I've already tried booting the pc into safe mode with networking and I lose the mouse and keyboard input (weird). Mouse and keys work fine booting into normal mode except they get r e a l l y s l o w after plugging in the network cable.
I've watched the processes' screen while watching CPU usage at 100%.
Except for minor blips here and there, all processes' showed 00. (weird)

 

[pgaiduk]

hold everything!
I've found it!
it turned out to be a either bad or miswired ethernet cable.
I didn't go there originally because my Mac Pro recognized the PC on the network as being shared but it just couldn't connect.
Go figure.
Thanks to the two who replied