When one computer turns on all other devices internet slows dramatically

[fergalmiller]

Right, I have 4 computers here all plugged into the same router by LAN connection. Recently I upgraded one of the computers, lets call it computer X, and ever since when i turn on computer X the internet goes really slow (enough for the computer to say its connected, but every website I try to connect to it times out) for every device. It never happened before on the old device. But heres the weird bit, even with the ethernet cable unplugged from computer X it still slows down the internet.

I thought it might be that if the power supply was bigger in computer X than the previous one then it could be draining it so I got an extension lead from all the way over from a different area of the house to see if it still goes slow, but it still does.
None of the computers have static IPs.
It might be useful to also note in the upgrade it went from Win 7 to Win 8.1
How does this work? There are no solutions anywhere for this that relate to my problem. Any sort of help or at the least education on how or why would be appreciated

 

[popatim]

Since it would be impossible for CPU-X to slow down the network otherwise while its completed removed from the network; it must be broadcasting massive amounts of interference.

Please list your systems specs with make and model#'s if possible. Include your router and or modem also please.