USB Wireless Slow

I am using a Belkin F5D7632-4 wireless router which I connect to my main PC via ethernet cable and get good speeds 6000kbps+. I also have a second PC downstairs which I connect to the router via a Belkin F5D7050 however, despite the signal strength being excellent, it refuses to go above 4000kbps in speed. It also seems to frequently pause throughput for a second then resume which you can see when you do a speedtest. I previously used the USB wireless adapter on a different computer (in the same place in my house) and had no problems, the wireless speed always matched the wired speed of my connection.

I have two belkin USB adapters, a v4000 and a v3000 but they both do the same thing, refuse to allow downstream speed of more than 4000kbps and the throughput is stop start stop start.

I am wondering if it is a problem with the USB ports of this computer because, like I say, I previously used the adapter on a different computer with no such issues. They are USB 1.1 ports but that was the same with the other computer I used which worked fine. The motherboard I am using now is an ECS K7S5A. I have also tried changing the wireless settings on the router (channel, wireless mode etc.) but that hasn't helped and, as I say, the signal strength is reported as excellent on the computer where the adapter is used.

Any suggestions as to what the problem could be and possible solutions?

Thanks.

bump.

If anyone has any suggestions that would be great, thanks.