Name of the Network Card, (can be seen in device manager) press windows key + r then type this; mmc devmgmt.msc . Don't worry this is a common issue when updating to 8.1
Try to find and install latest drivers. (most likely the driver is the issue here)
If we can't find a working one we might try and improvise by using some other driver by browsing > device manager > adapter > update drivers > (uncheck incompatible drivers,browse on computer > and select one available. Incompatible drivers actually do work! if a valid one is chosen. Kind of strange but some drivers listed as incompatible work in some cases better then the most recent one provided by your vendor
First check and see if troubleshooting tools will fix your problem, location below;
Navigate control panel and locate troubleshooting > network and internet.
Control Panel\All Control Panel Items\Troubleshooting\Network and Internet.
Select Network adapter, Internet Connection.