OT - BT Infinity/iMac problem

We recently changed over to BT Infinity broadband from Sky and, aside from various stability problems with the network generally, I cannot get my 2011 iMac to detect any networks to connect to. The modem and hub are downstairs and the iMac is on the floor above. We never had any problems with connections previously but aside from a period of about six hours when it was first installed, I haven't been able to detect any networks.
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I am running a MacBook Pro in the same room as the hub/modem and it always detects the available networks. My sons pc is upstairs as weel and that detects/connects ok however, my daughters windows based laptop cannot detect either.
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Is there any way do resetting something to cure this or does it sound like a problem with the hub/modem?

Turn the hub through 90 degrees.
Also check what wireless channel its on and change it.

happypig said:

Turn the hub through 90 degrees.
Also check what wireless channel its on and change it.

Click to expand...

Turned the hub and changed from channel 6 to channel 11. Made no difference to connecting the iMac or my daughters laptop.

Changed the hub security from WPA2 to WEP and managed to get the laptop running but still no joy with the iMac.

Took the iMac downstairs and connected it to the hub with an ethernet cable and it located all available networks and connected to t'internet.

Removed the ethernet cable and wi-fi connection was established.

Took the iMac back upstairs and it now finds all available networks and connects perfectly to t'internet.

So it would seem that plugging it directly into the hub somehow resets all the settings.

Hope this may help others who might encounter the same problem in the future.