If you upgraded to Win10 from 7 without doing a clean install, it's possibly a bad config between the two versions either in Winsock or Soulseek itself. A few things I would do:
Run PowerShell as Adminsitrator and run these commands:
New-NetFirewallRule -DisplayName "Soulseek" -Program "$env:LOCALAPPDATA\SoulseekQt\SoulseekQt.exe" -Action Allow -Direction Inbound
New-NetFirewallRule -DisplayName "Soulseek Out" -Program "$env:LOCALAPPDATA\SoulseekQt\SoulseekQt.exe" -Action Allow -Direction Outbound
Then, run these. May need to run command prompt as admin and not powershell:
netsh winsock reset
netsh int ip reset
ipconfig /flushdns
Restart machine, if that doesn't work, then reinstall Soulseek.