Internet connection slow on Orange Livebox

[Yodel]

I recently installed Livebox with one wirelessly-connected desktop pc and it was all working fine. The signal strength was not fantastic because the destkop is in the garden shed and the Livebox is in the house, but internet access was fast and web pages loaded very quickly. Next I connected a wireless laptop to the Livebox in addition to the desktop and although the laptop internet connection is very fast, the desktop is now really, really slow. Please can anyone tell me if there is a way to speed it up. If no-one can help I will have to face the dreaded Orange technical support!
Thanks in advance.