Wait, so you have multiple computers, wired and wireless, and randomly all the computers EXCEPT 1 PC goes offline? And its that PC that your playing a game on? Makes me think your have some QOS or port forwarding rules pointed to that one PC that is causing the issue. Or the game your playing. If you have DNS enabled on the router and you have a issue with DNS on the router's end, it would effect all the PC's equally. JMHO