You are using a wireless connection? That means you have a router. Make sure you opened the ports of your router in the right way or things might go wrong. You can read about router and everything with multiplayer here:
ClickCrash

Isn't it a funny old do...
We are familiar with all the many problems that can inflict the Multiplayer's life, involving the dreaded Modem ROUTER device, involving the opening or closing of various strange and magical "Ports", etc...

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...so I trawl through the various retail suppliers of "Modems", and do you know what; no-one offers a straight-forward, bog-standard, simple, USB Modem anymore?....(like my simple Thompson Modem ST 330)!....

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They are ALL complicated (expensive) "Wireless Modem Routers" now!...

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So, to all our many Multiplayer Chums out there, experiencing connection problems, dump that nasty Modem ROUTER thingie in the trash-can, find a simple USB Modem, plug one end into the computer and the other end into the phone socket, and away you go, no more problems....
...I still can't figure out why anyone would want to use a "Router" anyway!... :-?...!
...and a "Wireless" version just means that the toe-rag in the car parked outside of your house is tuned into your ISP and using your Service, for free....

....!!!
Paul...I love a "Simple" life.... [smiley=thumbsup.gif]...!