The Mo Creatures mod never works for me for some reason. Try deleting your bin folder, your resources folder, and your mods folder, and then force updating your game. That will reset your Minecraft client to its Vanilla state where you can try installing the mods again but there probably are conflicting mods which is the reason the game won't work. I believe all those mods are in the Feed the Beast mod pack which you can download here. Hope I helped you!