From this description I guess the problem is actually the router, have you tried to turn it off wait 20 sec and turn it on again. It's not uncommon for access points (AP) to be rebooted once in a while.
In Win7 there is a network trouble shooter, it's not the greatest but it might help getting closer to solution.
Yours
Zweiblumen
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Sodomy non sapiens. : I'm buggered if I know
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