You may just want to bite the bullet and delete any and all existing wireless profiles, and shut down the PC. Use the manual reset button on the back of the wireless router to reset it to factory defaults, then with a wired connection if possible (preferred) setup the router the way you want it setup the router the way you want it (SSID, Channel, etc,) hold off on the security and encryption. Boot up your problem machine and see what happens. If all goes well and the connection seems to auto-connect as you would expect after a couple reboots then go back to the router and define the security as you wish, and then on your computer edit the existing wireless profile to reflect the changes in security