BT Infinity slow and connecting keeps dropping out

Up until a few days ago I had no problems with my wireless internet connection.
Ihave Bt Infinity. I have two computers a desktop operating on Windows xp and a laptop.
There is no problem with the laptop and am getting download speeds around 38 to 40 Mbps
However on the desktop the download speed has dropped to 3 to 4 Mbps and the connection cuts off every ten or 15 minutes. The only way I can get it back is to unplug and reinstall my netgear adapter.
Any help on resolving this issue would be much appreciated
 
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