I put in a similar question a week or two ago, got a few attempts, but no real answer. We have a small peer to peer network, no domain controller, using static IPs and a pfsense firewall. About 6 months ago I bought a new Windows 7 machine, configured the ip address, the subnet mask, and the gateway, as well as 2 DNS servers. This machine works fine. Recently I bought another machine, very nearly the same hardware. I configured it the same (slightly different IP address of course) and it can connect to other members of the network, but no the gateway and has no internet access. I can ping this machine from the rest of the computers in the network. I can ping the gateway from the other computers in the network. It is configured identically to the other windows 7 machine that works. How can it be that the problem computer can ping other internal network addresses (e.g. 192.158.1.115) but can't ping the gateway at 192.168.1.1? Especially when the other computers can ping both the problem computer and the gateway? I used wireshark and it shows the ping requests going out, but no replies from the gateway. However, if I ping from the gateway, this problem computer replies. I checked the ARP tables on the gateway and this problem computers IP address and MAC address are there. The problem with not pinging is not the real issue. The real issue is that this problem computer won't connect to the internet - it claims that it can't get DNS information. But it can't because it can't 'reach' the gateway. What am I missing here?

Also interesting - I am able to connect to the gateway through Internet Explorer. I can log in and everything. What is preventing the ping? Why does windows report a DNS issue? There must be something that is stopping the computer from accepting ping backs, but not ping requests, stopping the DNS server replies that I believe are being forwarded by the gateway.