In a pinch, if you need access to your coins, you can install Breadwallet (iOS/Android) or "Simple Bitcoin Wallet" (Android only) and use your mnemonic/wallet words to restore your wallet there and get access to your coins.
If none of those methods work, you'll have to do it the "long way"... read here (Options 2, if you're OK with Python scripts... otherwise Option 3.) : https://bitcointalksearch.org/topic/m.19590212
In either case, I would recommend you migrate to a new desktop wallet like Electrum. MultiBit HD seems to be, for all intents and purposes, abandoned by the developers.
![Sad](https://bitcointalk.org/Smileys/default/sad.gif)