You may have either:
1) Installed a script which has overwritten the popups.ini file that is created when you install mIRC (it contains those popup menus).
2) Accidentally deleted the popups.ini file.
Type
//run $mircdir and check if popups.ini is still in your mIRC directory. If it isn't, go to
www.mirc.com/get.html and install another mIRC to a
different directory to your current mIRC. (So, if your current mIRC is in C:\Program Files\mIRC, you might want to install a new mIRC to C:\Program Files\SecondmIRC).
When mIRC is installed, open it and popups.ini will be created. Close mIRC again, go to the popups.ini file in your NEW mIRC directory and right click it, then click on 'Copy'. Then go to your OLD mIRC directory (the one with no popups.ini) and right click a white bit and click on 'Paste' (
not 'Paste shortcut'). You can then safely delete the NEW mIRC directory.
Now, when you open mIRC, the popups should be back in their rightful place!
Hope this helps

Regards,