There are several things that you can do in order to solve this problem. I suggest you download and install again the driver for your network card. You can find the driver on the official website of the manufacturer. Instead of restarting your computer, you can disable your network adapter and then Enable it. To do that, go to Start > Control Panel > Network Connections > right click on your currently active connection and select Disable and then Enable.
If the problem persists, you may contact your local Internet provider because this can be an external error.