This has me pulling my hair out! I have a windows server dishing out DHCP leases and a SonicWall NAT router. All clients work perfectly except for Windows 7 machines. All DHCP info is correct, DNS is working on Win7 machines. I can ping all internal addresses and the router but nothing on the other side of the router. This is true for both wireless and wired connections. I have tried disabling IPv6, it doesn't help. If anyone has any ideas, please help!
I later discovered when setting up a managed switch purchased on Ebay, that the web interface was set to the same IP address as the router. I should have checked it through the CLI before posting. I feel pretty dumb. It is still weird that it only affected Win7 machines. All works well now.