can not open only 2 websites

I have a client that has 9 work stations hardwired and 3 laptops wireless and 1 server hard wired and none of them can connect to 2 specific websites. The workstations are running Windows 7 Pro 64bit, laptops are Windows XP Pro and the server is Windows Server 2008 Standard R2 64bit. They were all able to open the 2 sites last Friday and now they cannot. I can ping and trace rout the IP address of the 2 sites and get no loss but if I ping/trace rout the site name it will not work. I know it’s not the sites that are having the problem because I can open it on my cell phone. But when I hook up my phone to their wireless I cannot open the site. If I put a static DNS IP of their ISP on the computers then I am able to connect to the 2 sites. I called there ISP and they said something must of changed in there network but I check all there settings and nothing has changed. I have never seen this before and am at a loss of what to do.

Thanks,
Dennis

Dwarf said:

Can they access the sites if the IP addresses are used as opposed to the name? If so, this is a DNS issue, specifically the DNS servers currently used aren't capable of resolving the names of these sites into their actual IP addresses.

Make a note of the current DNS settings in the router, and change them to Google's on 8.8.8.8 and 8.8.4.4. If that works, then the problem lies with the ISP.

I will try that. But when i was on the phone with the ISP they said they were able to open the same sites and they use the same DNS that is set in my modem/router.