Have you been recently told by a popup that you must install flash or some other program in order to watch a video?
The quick and dirty is to go to your device manager goto network adapters find the adapter youre using whether is wired or wireless and uninstall it..
then click action on top of device manager and click scan for hardware changes, and it will refind and reload the driver with its default settings..
If its wireless, you will need to reenter your wifi password when trying to connect..