Yosemite One User Hangs After Login, Other Works I turned on my computer yesterday to have it hang after login with user A. The desktop loads but (sometimes my icons appear, sometimes they don't) but as soon as I try to do anything with my mouse, it goes circle wheel of death. 

However, when I login with a user B, everything loads fine. (Of course, all the files I need are on the user A login. I barely even knew I had a second user account until I started trying to fix this as I had an auto login setup.)

I've done the disk utility repair disk and repair permissions, as well as the PRAM reset and SMC reset. Also did a "reset home folder permissions and ACLs" and the parental controls tricks per this post: One user can&#39;t open anything after Yosemite upgrade   I've even uninstalled a ton of apps.

None of it helps. I've also booted into safe mode. And it's the same problem, user A hangs after log in.  

I'm currently re-installing Yosemite (5 hours left, this is ruining my day).

If this doesn't fix the problem, does anyone have any other suggestions? Or if you've had this issue, how do I prevent it from happening again?

I'm using an iMac if that makes a difference.
You have just duplicated the first part of the "why is my Mac crashing?" troubleshooting steps.

If it works fine under one user and the other user, not so much then the problem is not with the O/S it is something specific to the user.

Steps to fix this include booting into Safe Mode (hold Shift while booting) and logging into that account. Take the contents of that users Library/Preferences folder and put it in another folder on the desktop. and reboot normally. If that fixes it one of the many preference files was corrupt. If not...

Then there may be something installed in that user's account that is doing something bad. Go into System Preferences -> Users and remove the startup items for that user and reboot.

There are a lot of things that this could be. And it is a matter of finding what is unique to one user account that is crashing. It's a lot of fiddly, annoying investigations. It might be easier to just create a new user account, move only the necessary stuff to the new user profile and delete the old one.