Ports are all forcing themselves closed.

I have a standard PC => Router => Internet (Modem) connection at the moment and I didn't notice until just now but every single port on my machine forces itself closed. I know the issue is not with my ISP as they don't block any ports, I have had ports opened before, and as of noticing this issue opening ports works on my other PCs. After testing the router is also functioning perfectly and is not at issue with port forwarding.

I do not run any type of anti-virus software and I also do not run any third party firewall software. Windows Firewall has been tried as both enabled and disabled (though they give different results). When connected to the internet through my router the opened ports appear as stealthed like all of the non-forwarded ports when windows firewall is enabled with proper rules and as closed when windows firewall is disabled. When connected directly through to my internet the ports all show as closed. (using ShieldsUP!)

The other machines are both running Vista Ultimate x64.

*Edit: The machine I am having this issue on is running Windows 7 Ultimate x64 and I have been able to successfully open ports before.