Next have them do a ping 192.168.1.1, this will ping the CMTS unit, this should never fail. Times where I’ve seen this fail is bad Ethernet cable, bad network card on modem or PC or firewall on PC. Pretty rare.
Next have them ping 192.168.1.254, this pings your router. No response on dropped packets on these ping indicate that the router is not functioning properly. Again doesn’t happen often, but sometimes these routers will lock up and not respond to pings and have to be power cycled.
Next ping 220.127.116.11 which is a large DNS server that I’ve never seen offline in all my years. If they can’t ping this address or there is dropped packets then there is problem with the internet connection that feeds the router. Most likely your DSL/T-1/Cable Internet connection is down.
Next is to ping yahoo.com. If you get a message saying it can’t find the host yahoo.com then there is an issue with the DNS servers. Again we use very large and popular DNS servers, but always prefer to use your ISP’s DNS servers if they provide any for speeds purposes and so if they do go down then they can be held accountable. This ping should resolve yahoo.com to an IP address and should get replies.
At this point we know there is perfect connectivity between the PC and Internet, but to determine if they have a browser issue open up their favorite internet browser and verify that they can reach multiple websites. If they can’t then the problem is with the browser and it’s settings. There are countless things that effect this, mostly malware and viruses but also antivirus programs that setup the browser to surf through a proxy for “safe surfing”. I’ve seen this countless times, Norton Internet Security is usually the biggest culprit when it comes to this.