My Windows HP 8.1 computer will not directly connect to a Comcast XB3 (Cisco DPC3939 Docsis 3.0) gateway by either ethernet cable or wireless. When this same computer is connected to the XB3 via a Cisco Valet router it connects both via ethernet and wireless to the internet. Five other devices all connect both by ethernet and/or by wireless. These include: a Windows 7.1 HP laptop, a Windows 8.1 HP desktop, a Google Nexus 9 tablet, and two Google Nexus 6p phones. I have searched several knowledge bases and attempted recommended fixes including resetting and clearing the IPV4 settings and turning off the XB3 firewall. Nothing works so far.