DMZ (De-Militarized Zone) basically removes any kind of protection that the router may be providing (port forwarding, firewalls etc.) to a specific IP or part of LAN. It means you are sort of cut off from the rest of the network as well, and almost treated like you're part of the internet (very vaguely).
To be honest, with all the settings you have tried disabling I doubt that this would provide a solution; however you could try. Again this may leave the computer at risk, and I would revert if it doesn't work... Although if you have a decent firewall, anti virus/spyware running you should be fine.
