You might see if this works:
Clearing Caches to Fix Login Problem
You will need to type some Unix commands. If you are not comfortable with this, I don't know of anything other than a re-install. But if you are careful, you should be OK. I recommend you print this out in a largish mono-spaced font so you don't miss any spaces (or add extra ones). Note that case is important.
Be careful. Some of these commands are dangerous, since you are going to be root.
Start up in Single-user Mode. When this has finished you will see a prompt ending in '#', although there may be other messages. Enter the following commands after the prompt:
Press RETURN. Wait a few seconds for 8-10 lines of output. If the last line says repairs were carried out, repeat this command until you get a message 'The volume <yourdiskname> appears to be OK'. Then continue with:
/sbin/mount -uw /
rm -r *
rm -r *
Press RETURN after each command.
This should now take you to a proper login screen after the normal boot sequence. You should then Repair Permissions by using Disk Utility (in your /Applications/Utilities folder).
This seems pretty dangerous and I don't want to do this unless someone can confirm this is the problem. Any other ideas?
I've read that a lot of people are getting to a login screen where they can enter a username and password, but for me, I only see a screen asking me to chose which login, but aside from the icon for login being selected, nothing happens past that.
Then I suggest you try reinstalling. Restart the computer and after the chime hold down the OPTION key until the boot manager screen appears. Select the Recovery HD icon then click on the downward pointing arrow button. When the menu appears select Disk Utility. Do this:
Repair the Hard Drive and Permissions
After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the menu.
If DU reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.
Select the Reinstall Lion option and reinstall Lion.
If this does not fix the problem for you, then I recommend you erase the drive and make a fresh installation of Lion. Restore your data from your backups.
I've tried everything you guys have said already, except the cache clearing but none of that worked. Here's what did work so far:
I opened terminal from recovery mode and typed resetpassword. This allowed me to access root, which wasn't showing up during login. I reset the password and permissions options and restarted. Now there is a new icon for "other users" which allows me to enter root and log in. This gets me into the OS as root. I can then switch users to my original user, HOWEVER, upon restart, my old users still do nothing when I select them. No password prompty or anything.
Whatever the issue is, it's only in login, because my users work fine in Lion once I'm booted in root. Anyone know how to fix that?
Just to confirm you are not alone, not that it helps, I have the same issue. I installed Lion on my MacBook Air (late 2010) and all went well. A bit hesitant, I did the same on my iMac 27", 16GB RAM, 256GB SSD+2TBHDD with wired apple keyboard and the wireless magic mouse, but things stopped at the login screen. While I can move the mouse around on the screen, I can't click anywhere and the keyboard does not react to anything. The password window has the light blue around it as if it was selected. I only have one user account created so I do not see anything else.
I managed to log in once via Screen Sharing from the MacBook Air, but when I rebooted the iMac the same probleam appeared and I couldn't get to the iMac via the MBA anymore.
I restarted the iMac several times and at times it would let me log in. I noticed that when after the restart the iMac showed "Mouse Connected" I was able to log in and use the keayboard to type the password. If that didn't show, I was stuck and had to restart.
I did reboot into the Recovery partition (by holding Alt during restart) and repaired permissions but this did not help. I also rebooted to the Recovery partition and Reinstalled Lion, but the problem remains the same.
I do not have a solution, but just wrote all details so there is more info available. Any help is greatly appreciated!
@Gordito73: You're not alone, either. I encounter same problem while rebooting my Mac mini and being stuck in the login screen. With Apple bluetooth keyboard, I could select different commands by pressing Up/Down keys, but the "Return" key never functioned. Also, my Magic Mouse didn't react at all.
This problem also came to my MacBook Pro (Unibody, 15"). The Return key on MBP didn't function, and neither did the trackpad. In the end, a wired mouse solved this problem.
How could this happen, I wonder. Apple shouldn't have let this come stupid.
Same thing happened to me. Do this.
When you are at log in screen and it won't respond when you are clicking on the the user icons -
This will bring up a generic login field. Enter your name and password - boom you're in!
I had to first remove my password in System Preferences under Users & Groups This would allow Lion to boot up directly, bypassing the login screen.
I then added my password back in system preferences and I am in business! No more problems to this point.
Hope this works for you!
I don't know if removing and changing my password was necessary. It is just the sequence I went through. The solution may be this:
Under User & Groups, select Login Options (has little house next to it).
In the Automatic login field, select your name.
This should cause Lion to bypass the login screen when booting up.
After doing this I was able to go back in and turn Automatic login off. Now at login I get the user login icons at boot-up. When clicking on them the password field now appears.
I have a similar issue. When I enabled Filevault 2 on the whole disk, my Apple Wireless Keyboard and Magic Mouse would no longer function at the welcome screen. When I turned off Filevault, they worked at the Welcome Screen again.
Also, when trying out the workaround on this discussion, my Autologin is greyed out and I can't select it.