Are you referring to the "Log Files" item in the Tools menu?
In previous versions of mIRC, this opened a Log Files dialog that you could use to search through your logs. This was changed in mIRC 7.1 to open your Log Files folder in Windows explorer, since I assumed this would be more useful to users.
However many users requested that I add the Log Files dialog back (see earlier thread on this topic in this forum), so it is now back in mIRC v7.14.
If you want to open more than one file, you can click the "Edit" button in the Log Files dialog - this will open the log file in your text editor.