sounds like a weird one, only advice i can give, is make sure you have all the latest drivers for you graphics and sound cards, and that directx is up to date. if you have something like norton av, then you might want to disable that too, for information on router configurations you can check the official website, which should explain which ports need to be open etc. failing that, make sure there are no programs running in the background that might be interfering, like limewire etc.
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