BleepingComputer.com: Wireless connection (with Sky broadband) continually cuts out, but only on certain computers.

Hi,
First of all I apologise if this is a little vague, my knowledge of these things is limited. :/
The problem has become incredibly frustrating to the point that I can barely use the internet.

3/4 weeks ago our household switched to Sky broadband and I've experienced problems ever since.
The connectivity will cut out after a few seconds or minutes, or, at best, after 20 or 30 minutes.
Despite repairing or refreshing the connection, it's always difficult to re-connect; either the connection will cut out as before, or it can take up to 30 minutes to connect.
During this time, I'll be alerted that it was "unable to connect to preferred wireless network", or that no networks were found. This is despite the list of available networks displaying our network with enough signal to connect.

However, this is only a problem on my own laptop. There are two other laptops accessing the same network, all with few problems (the odd disconnection but nothing unusual).
It may be important to note that this particularly laptop is situated downstairs and the router is upstairs, though when these other laptops are downstairs as well, they don't experience the same problems.
Even when my laptop's connection is stable, the speed will be at around 9 or 18mbps, whereas on the other laptops it is around 54mbps or higher.

I would assume this is a specific problem with my laptop, but with previous wireless connections there's never been an issue...
Either way I'm completely clueless, so any suggestions or solutions are greatly appreciated. Thanks.