I understand that your annoyed with things going on here but can you please just state the symptoms and how the pc's are connected to the router.

do the systems both connect to the internet if only one is switch on ?

if they are wireless do they connect to the net when hard wired ?

Can you access the router configuration from both PC's ?

what do both pc's display when you enter the command prompt (start, run then type cmd) and type ipconfig /all