Hi Dougnut,
Usually this is due to a router or DSL modem that has router ability. In order for this to be resolved you must forward the ports (open ports for WinMX to use) in the configs. Its not usually difficult thing but takes a bit of time. Have a look at this page and it will help you to get started.
https://www.winmxworld.com/tutorials/routers_info.htmlThis will then direct you to another site
www.portforward.com to find your model and get specific instructions for WinMX.
Once this is finished your uplaods should work fine if your WinMX is also allowed in any firewalls your using on the PC.
If you need more help or have questions about this procedure just post back here.