Usually this issue will have little to do with the operating system or the specs of a PC, other then if any static IPs where set up in the Network confurations. Which I suspect the IP Address assigned to this PC could/would have changed upon this reconstruction of yours lol
So thats the first thing I would check because uploads/ and search results will be a port/firewall issue.
Downloads however are not related to ports and I suggest that you may have some other settings not quite right or this can also be because your not using a filtering patch like the ones from:https://patch.winmxconex.com/
If you are its going to be settings, if WinMX will connect it will download. (once a file is found lol).
Try checking your router configs and your network connection for the correct IP address.
Go to Start > Run > type cmd
A new black box will appear, in it type ipconfig
Then hit Enter
You will now see lots of information, of this you want the one that says 'IP Address
' (IPv4) Make a note of it.
**Note: not to be confused with the 'Default Gateway Address'.
Close the box.
Go to the router settings and verify that is the same ip still used in what rules you have. If not fix them and try your searches and uploads.. see how that goes. If the ip is correct then I'd suggest rechecking any protective software you have on teh system, firewalls, windows defender, etc and make sure those all have WinMX allowed also.
Let us know ...