I have a Windows 7 x64 Professional PC that is set to allow incoming remote desktop connections. Until a few days ago this was working perfectly, but without warning it has started to refuse connections that are targeted at its IPv4 address - the system attempting to establish the connection just times out. The system is not set to require NLA.
Bizarrely, when using the IPv6 address, it accepts the connection and works normally.
I have verified that all the services are running, and that it is listening on port 3389 (both IPv4 and v6), and have tested without any firewall turned on - same result. Since the problem manifested, I have installed Win 7 service pack 1, which has made no difference. All other incoming IPv4 connections are accepted normally (file sharing, TFTP, etc).
Please advise the next steps I should take to troubleshoot this. Thanks in advance.