If so, what have you done to the machine? Have you tried system restore?
BTW, WEP is old hat and can be hacked in about 20 seconds. You need to change to WPA/WPA2.
You might also try tweaking it. Go here http://www.broadbandreports.com/tools Run their speed test, make note of the results. Not run the Tweak test and note the recommendations. Run Dr. TCP and make the adjustments. Reboot and run the test again.
I have 2 computers at home. A laptop and a desktop. Both access the internet via a WEP enabled wifi device. Recently the desktop has seemed much slower in accessing the internet. I ran bandwidth speed tests with them side by side on speakeasy.com and the laptop speeds are 3.5 down X 0.9 up. But the desktop that connects to the same wireless device is only getting 0.5 down by 0.9 up? I've tried changing network settings, but I still can't figure out why the laptop is getting the full bandwidth and the bandwidth on the desktop is getting "choked"?