Windows 7 Ethernet Network problem

Question

I have two machines (laptop/desktop) with Windows 7-Pro setup. When the laptop is using its wireless interface, the network works as expected. When I plug in the ethernet, the machines refuse to communicate.

• Both machines and router on 192.168.1.0/24 network
• Both machines have valid IP addresses, and can ping router.
• Both machines can connect to the web fine, so machine -> router -> interweb is ok.
• Both machines are running in 'Work Network' mode.
• Both machines are not in a homegroup.
• Windows Firewall is off on both
• IPv6 is off, v4 only.
• On ping -t -w 1 OTHER_MACHINE, I get a response for about every 15th ping, on both sides.
• Wireless card is disabled,hardware switch and software,(in adapter settings,disable) on laptop.
• Telnet to desktop port 80, from the laptop fails, connection refused.
• ping desktop and ping -a 192.168.1.11 both resolve,as in the first converts to an IP, the second to a hostname.
• Route tables look ok, but I'm not an expert on this.
• tracert desktop sometimes works. sometimes it comes back right away, other times it times out.
• I have rebooted both
• I have changed ethernet cables+router ports, (even though both machines can connect to the web fine.)
• There's no special rules/blocking setup on the router. Its just a standard router/AP combi.

I don't have another non-Windows 7 machine to check things on right now, I hope someone here can save me the trouble of going and hunting one down. Perhaps I'm missing something obvious.

Edit Since I cant comment yet.

• No AV software on either machine.

Answer 1

Antivirus software can sometimes do this kind of thing, especially the fancy kind that claims to defend against internet threats. They run their own defenses that may not be called a firewall, but function much the same way.