Trose,
Check to make sure that your internal IP hasnt changed, the IP is the one the router would assign to the machine your on, when you forwarded ports for WinMX to use.
Go to Start > Run > type in cmd then click OK.
In the black DOS box type ipconfig and look at your Default IP Address.
Open your router web based homepage as you would when forwarding and make sure that number in your rules matches. A few router dont require you enter that info but, most do. Sometimes out of the blue a shut down and reboot can cause that to change, basically killing any rules you had set up.
Let me know..Also while your there might as well make sure the ports you set match those in the WinMX settings for Incoming TCP and IN/OUT UDP too.