It sounds as if you may need to reset your password...
Resetting User Password in Lion, Mountain Lion & Mavericks
Boot into your Recovery Partition by hold down the Command and R keys whilst booting.
When the Recovery screen appears, go to the Utilities menu and open Terminal.
In Terminal, type:
...a small app will open and allow you to choose the user for whom you want to change the password. If you are the admin, be certain that you choose your admin user. Type in your new password twice and give yourself a good hint. Click OK (or Done or whatever) and reboot, enjoying the use of your new, hopefully memorable, password.
I agree with Linc.
Boot to safe boot, but when you're in there look at:
1. While in safe boot, go to System Preferences > Users and Groups > Login Items.
2. Look at the list of login items, these are all things booting with your computer. If you see anything you don't need starting with your computer, remove it from the list by selecting it and pressing the - underneath.
3. Reboot your computer.
Let me know if that helps.
Anyone ever find a solution to this? I have the same issue.
Upgraded to Mavericks. Everything worked like a champ before.
Now it is stuck on the Login Screen.
I type password and hit enter.
Screen flickers (not like a bad password was entered), goes all white, then back to login screen.
Same result if I try to log in as guest.
I have reset the password doing the "resetpassword" thing, no change. Can't log in.
Haven't tried safe mode yet, but will when I get home today.