My Mac gives me a black screen after logging into one account, but not another Whenever I start my MacBook (mid 2009, running OS X El Capitan 10.11.6), like any normal day, I click on my main account and log in. 

Today, when I tried typing in my password, it let me in as usual but I get nothing but a black screen with the spinning beachball cursor. However, I can log in to my other account perfectly fine. 

I've tried booting into safe mode and logging in but it just gives me the same result. I've also run First Aid on the disk, but that didn't resolve the issue either.

How can I troubleshoot this further?
Removing the user/library/preferences could help, however, if you still have the same issue and booting in safe mode has not solved the problem, means that the user is damaged.

so try removing user/library/caches

if you still have the problem, the fastest solutions are next:   


restored a time machine backup to a date where issue does not exist if you have one.
create a new user as administrator, sign into this new user and from finder transfer the content from the old user to the new one. 


note: in this step you tested that preferences were not the caused of the problem, so moving the content of this folder from the old to the new one will bring you all the settings into the new account. Also note that apps are open from all users, so you will not have to install any app either. the only thing you would have to do is to set up the mail accounts in mail app from the new user.