Possible R6100 router problem

I have an R6100 router connected to a cable modem. I have three pc's using the router: a desktop wired to the router, and  desktop and a laptop connecting remotely to the router.

 

I have normal access to the internet with the laptop - which is just 6 feet from th router. I have questionable access to the internet with the desktop that is way across thr house - but that is sort of normal, so I'm not overly concerned about that connection.

 

But I have no internet access with the hardwired pc - which is running Windows 7 Professional.

 

The Windows troubleshooter doesn't seem to be much help - it appears to think it may be a firewall issue - I've made no conscious changes to the firewall settings. The desktop also uses McAfee Livesafe - I don't see anything in LiveSafe indicating a current problem.

 

Could this be a router problem?  If not, does anyone have a suggestion for what I should look for?