Try different USB ports or different computers and check if the adapter can be detected under Computer Management----Other Devices or Device Manager.
If nothing, your adapter should be defective. Is it still under warranty?

i didn't explained my self right.
the adapter works for sometime and then suddenly the computer can't find him. i checked the Device Manager and the adapter doesn't appear there.

thanks

Did you check Other Devices? How did you make it work again? Unplug it and plug it back? Is it possible for you to install it on a different computer?
What's the operating system?