try setting up a new user and try to connect on that. TBH ive seen things like this screw up networking on various occassion I tend to just say stuff it and format otherwise as in this case you will be pulling your hair out. It could be a screwed registry which witha bit of luck the new user will not be subject to. You may well have to bite the bullet
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http://www.snapfiles.com/get/winsockxpfix.html you could try that if you are running xp