Download and install rootsh from extras.
Open terminal and type root
Then type vi /etc/mce/mce.ini
Scroll down to this line:
PowerKeyShortAction=menu
Press I to enter input mode, remove menu and type tklock so that it's:
PowerKeyShortAction=tklock
Press CTRL+C to exit input mode
Type :w to save the file then press
Press CTRL+Z to exit
Type stop mce then start mce

Remember to remap the menu to something else (double click/long click w/e)

P.S. don't use caps, if someone has an answer they'll post it