Sounds like you need to get the drivers for whatever device it is. If you right click on My Computer and click on Manage, then click on Device Manager down the left hand side. Any device not recognised should have a question mark by it, and it should tell you what sort of device it it (multemida, networking etc..)
Or just use the drivers disk. Put it in your CD drive and then right click on the device that is not known. Click on update driver, and follow the wizard.
Oh right...well that wouldn't be related to your USB problems, as the ethernet device doesn't use a USB port.
I need more information about the USB problem before I can help you...like when it happens and if it's happened since you plugged something in etc...
And if your ethernet device has a red X through it, then it's not working, might be the device or the drivers. Double click on it and it will tell you what's wrong.