The Original Question states the Preferences are inaccessible.
Presumably as you have joined this thread that is also your Starting point.
Here is a Thread that deal specifically with Messages not opening as the AppleGothic Font is missing.
Re: My messages won't open at all on my macbook pro.
Turning Off or removing Fonts from th Hard Drive name/System/Library/Fonts (System Fonts) will cause issues all over the OS if they are missing.
Some Alternative versions installed by some third party apps can case duplicate issues.
There are also Fonts in Hard Drive Name/Library/Fonts which can be a mixtures of Apple Installed and User Installed but for use by Every one (every Mac User on your computer)
There is also Hard Drive/Users/(yourShortname)/Library/Fonts where you can install Fonts you only want yourself to have access to.
This thread goes on to talk about having 2 Step Verification set up with Apple and FaceTime needing this.
You have not mentioned that so I did not bring it up.
As the Original Post is 3 years ago it may also pay to start a new thread.
8:18 pm Tuesday; October 4, 2016
iMac 2.5Ghz i5 2011 (El Capitan)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
iPhone and an iPad (2)