This is a normal problem that happens to a lot of people.
The first thing I have to say, is re download FH. BEFORE you do DELETE it, or else it will not replace itself, therefor not fix the problem.
Also, if that doesn't work, that means something is either in the wrong folder, or it is just very laggy.
Check all the folders that you might have moved downloads too.
Also, check your particles, and make sure that there are none labeled _0 or _1
If those work, when you open the game again, open the options menu, and turn the view distance to 0, and turn off the water reflection. That should help the lag that is playing a part in the crashing of your game
I hope these help!