I'm having exactly the same issue at home. When I turn on my HP Compaq Presario laptop it is intitially saying that no network is available. If I then move the laptop to right beside the wireless router, it finds the network and connects. I can then move the laptop back to where it was originally, where it tells me the signal strength is excellent.
I have updated the wireless adaptor drivers, and it's made no difference. This was happening very occasionally until about 2 weeks ago; now it happens every time.
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