Can't log in as admin

[OneEyed55]

Hello! I have a Macbook Pro Early 2009, Mac OS X Mountain Lion and I am facing the following problem:
After downloading (from the official website, not from App Store) and while installing ClamXav, I tried opening Safari, but it said that some necessary plugin was missing and that I had to re-install Safari, even though 1 minute before that it was functioning normally. The menu bar became unresponsive and I couldn't even force quit the ClamXav installation. I pressed the shut-down button and when I turned my MBP on again, it wouldn't log in as an administrator (note: I installed ClamXav as an admin), but it would look as if it were loading and then freeze, so I had to hold down the shut-down button again. However, I could log in as a Guest User and that's how I uninstalled ClamXav using AppCleaner (though I think it only deleted the app from the guest user account) and later ran Disk Utility to Repair Permissions. No luck. I tried logging in in safe mode, but I still wasn't able to log into my account. I left it loading for about 40 minutes and it never logged in.

Any suggestions? Thanks in advance!

 

[ConCat]

First-off, I'd like to make you aware of a safer force-restart. Cmd-Control-Power Button. It gets the job done, but it allows for some things like disk cache flushing and other things. I'd suggest first booting into recovery and trying a disk repair. If that doesn't work, just reinstall the OS. It won't overwrite your stuff, just system files.

It may not work though, in that case the solution will either be complicated or notsomuch. I'd like for you to also run a hardware test. I believe the shortcut is command+D when you turn on the computer. Don't be afraid of the strange Mac OS 9 UI. I can't explain it, but I suppose it doesn't really matter, eh?

 

[OneEyed55]

You mean that whenever I can't get it to shut down from the Menu Bar, I should press Cmd-Ctrl-Power Button to turn it off safely? Thanks for the advice!

I have tried the disk repair (didn't make any difference) and hardware test (everything appeared to be OK).

Won't reinstalling the OS delete any files? And besides, my MBP came with a different OS than I'm currently using, as it has been updated.

 

[MisterKeeks]

Won't reinstalling the OS delete any files? And besides, my MBP came with a different OS than I'm currently using, as it has been updated.

Do you have any sort of backup (Time Machine, Carbon Copy Cloner)?

 

[OneEyed55]

Time Machine, yep.

 

[GGJstudios]

I uninstalled ClamXav using AppCleaner (though I think it only deleted the app from the guest user account)

In most cases, app removal software like AppCleaner doesn't do a thorough job of finding and removing files/folders related to deleted apps. For more information, read this and this. If you just want to delete the app, drag the .app file to the trash. No other software needed. If you want to completely remove all associated files/folders, no removal apps will do the job.

The most effective method for complete app removal is manual deletion:

Best way to FULLY DELETE a program​

 

[OneEyed55]

Launching Activity monitor and after switching to "All Processes", I noticed that there's a "kernel_task" running through the root user.

PID: 0
Process Name: kernel_task
User: root
%CPU: 0.9-2.5 (flunctuating)
Threads:77
Real Mem: 415.0 MB
Kind: Intel (64-bit)

Isn't root my administrator account? Since I cannot log in to that, how come this kernel task is running? There's more processes running at the root user as I can see in the activity monitor, but this is too big considering that I haven't even logged in there. Could this kernel task be the problem? I suppose not. And why can't I quit it?

And anyway, is it possible that one of the tasks shown in Activity Monitor may be what's preventing me from logging in as admin?

 

[GGJstudios]

Launching Activity monitor and after switching to "All Processes", I noticed that there's a "kernel_task" running through the root user.

kernel_task is part of Mac OS X. It's always running, no matter how you're logged in. If you don't know what a process is for (there are many related to OS X) then don't try to shut them down.

 

[OneEyed55]

I figured that, yes. Maybe the only solution is to backup the disk and then reinstall OS... I can't find any other way.