On my laptop keyboard (Ubuntu 10.04) keyboard lock is currently On.
$ xmodmap -pke|grep 77
keycode 77 = Num_Lock Pointer_EnableKeys Num_Lock Pointer_EnableKeys
keycode 177 = XF86Phone NoSymbol XF86Phone
$ xmodmap -e "keycode 77 ="
Voila ! numlock is now disabled.
xmodmap -e "keycode 77 = Num_Lock Pointer_EnableKeys Num_Lock Pointer_EnableKeys"
Puts it back again. (Maybe greping for Num_lock would have been a better idea, but you get the gist).
Reply to @Martin Vegter's comment.
Ok, in reply to your comment xmodmap ruins your bindings, understood.
I have just checked the Openbox Documentation
Take a look in ~/.config/openbox/lxde-rc.xml
ls -l lxde-rc.xml (do you have an rc.xml as well ?, please check ).
take a copy of it as backup
(use an editor) search for numlock (maybe nmlk).
Do you see something like this ?
Comment it out OR change The keybind key-value to an alternative eg Alt-Numlock to toggle
To Comment out
<!-Commented out from here
To Here -->
Change to Alt+Numlock toggle
save changes and logout/login or restart.