Start Network and Sharing Center.
In the Tasks pane, click Manage wireless networks.
Right-click the connection you want to delete, and then click Remove network.
In the Manage Wireless Networks - Warning dialog box, click OK.
Reboot router, connect your computer to your wifi, rekey-in password.
If still cannot, reset your modem.
This happen could be IP conflict where your router might not able to assign DHCP to connection devices.




