Can you confirm you are able to dns resolve Start > Run:
cmd /k nslookup

You can also ping

I'm not sure if your firewall can be queried with PowerShell, but are you sure there's no block on mirc.exe?

Get-NetFirewallProfile -Name Private | Get-NetFirewallRule | Where { $_.Action -eq 'Blocked' -and $_.Name -like '*mIRC*' }

Note: You may also run this with -Name Public

GNU Terry Pratchett - Looking for a mIRC help channel -> Check #mircscripting @