I'm going to give a quick summary then give all the details that I can. I just started working on this problem and don't have access to all of the details.
Summery: New workstations have been replacing failing ones over the past few months. When these new workstations were installed they couldn't access the internet. Internal network functions fine. The first workaround was to reboot the machines and then the internet was able to be accessed for a few days then the problem would come back. The NIC cards were changed out from a PCI-X to a PCI to see if that would make a difference and it did not. The second work around that is being used now is to do a "get and send mail" with outlook. After that is done the pc will be able to access the internet. This will only fix the problem for a few hours to a couple of days. At first it was only the new workstations but a couple of a weeks ago an older workstation has started to have the same problem.
Each workstation has two network connections, one for the internal network that sends everything back to the HQ over vpn and the second which is used to access the internet.
I tried to ping an internet IP address (to skip a DNS lookup) from a workstation that was not able to access the internet and it still timed out.
I looked through the router / firewall logs at each site (there is six) that is having this problem and couldn't find any log error that would indicate a problem.
The router / firewalls being used are Sonicwall TZ180s and TZ210
DHCP is turned off and the IP's are static.
I was told no changes have been made to the routers / firewall since the new machines have been added.
That is just about all the information that I have at this point. I guess the big thing that stands out is that once you sync with outlook the problem goes away for a bit. Any help would be greatly appreciated.