So I booted up msn, and all looked normal. Those with coloured names still had their names coloured on the online list. However, one talked to me, and it doesn't colour it in the window.

Then I realised that the plus drop-down menu was missing, and none of the commands work. And none of the right-click options work. And tabbed windows aren't working.
I uninstalled it, then reinstalled it. Didn't work, colours are all still there on the online list, but that's all.

I'm still using 8.5, and haven't done anything out of the norm. Anyone have any idea what's gone wrong? Thanks for any help.

Can you verify that a file called "msimg32.dll" is in the Windows Live Messenger root directory (default: C:\Program Files\Windows Live\Messenger and C:\Program Files (x86)\Windows Live\Messenger on x64 machines) and you have no other add-ons like SweetIM installed?

You also might want to update to WLM 14 to see if it works. Some skins remove the Plus! buttons from the toolbars, although I don't know whether that should affect chat tabs.

I do indeed have that file, and I have only ever installed plus.

I'd rather avoid updating if possible, I tried it before, and I hated it. Anything else that could be wrong?

Huh. It seems to have resolved itself, three reboots later. Bizarre. Thanks anyway.