Many shared hosting enviroments block ping (ctcp) requests to the main host or IP, so this is nothing uncommon.
Just to clear you up there, ping from the DOS command line is not a CTCP ping. It's either a UDP or ICMP ECHO. CTCP is an IRC thing. You were correct though, many block ICMP ECHO.
Check your firewall (sic- should be named proxy) settings in mIRC. To disable your mIRC firewall configurations: /firewall off. Try to reconnect. If you are still unable to connect, try resetting your router. To do this, turn the power off for your router. Count 30 seconds, then turn it back on. Wait for your router to reconnect to the internet, and try again. This is important because many routers cache DNS entries, as does your OS, so in actual fact ipconfig /flushdns
might not be doing what you want it to do.
If this does not help, please report back with the results of /dns irc.torn.com.