As rolli59 said, make sure you install the correct driver from your network card's manufacturer's website.
If the correct driver is installed properly, what I would try is to unplug the power cord connected to your desktop after shutting down properly, and press the power button 3 times, then plugging the power cord back in. If you have a laptop, take the power cord and battery out and do the same thing.
Let me know how things work!