Firstly, please don't reply to your own post in such a short period of time. Message boards across the Internet, including this one, are not "real time", threads get replied to when someone is available.
Secondly, mIRC does not open with any song. If your mIRC is playing a sound of some description when it opens it's because you've got a script. If you downloaded mIRC from anywhere else except here, you've got some script which lamely packed the mIRC.exe with itself.
In this case, you'll have to speak to the author of the script and ask them, or if there are any lyrics with the song put them into Google.
Regards,