I had a similar problem, where my laptop'c connection worked fine, but as soon as my desktop's wired cnnection was connected to my wireless router, too, the wifi connection died.
Check your computer for viruses and spyware that might be flooding the network with packets... I did a complete scan of my esktop, found something trying to access some german website, banned the site, got rid of the programs it infected (it wasnt even a virus program, but it seemed to have been corrupted by it) and now the connections are working fine...
May or may not be the same as your problem. but I figured Id post it. Mine was a netgear router.
