That might help you get in and see what is going on.
Your Admin account may be corrupt and the easiest solution is to create a new one and move on.
Rebooting while holding down the Command + S key may help too
I have a MacBook Pro that I believe is approximately a 2006 model. It is running OS X Lion. The problem I have just started this evening.
I was using the laptop and some applications were not working properly. I tried to open an app called Things and also Word. Both would bounce in the dock like they were opening but then would stop and never opened.
I then rebooted the mac because of this and have been unable to get in since then. When it gets to the login screen I have an option to log into my ID or as Guest. I choose my ID and enter my password and press enter. It acts like it's logging in but then goes to a white screen with the pointer and then back to the login screen like I never logged in. I then of course click on the icon for my ID once again and enter my password for the same thing to happen again. It's like an endless loop and takes around 10-15 secs with a white screen and goes back to the login screen.
I'm not sure if this is connected but for the last 1-2 months I've had this issue with it freezing up/rebooting. It seems to happen when I am running many apps at once or doing something else that's very intensive. Often what I experience is the entire screen locks up or the dock locks up. Sometimes it will just turn off, sometimes it will reboot, sometimes it goes to a black screen with a lot of white writing where I need to restart. Some days it happens several times a day and other times once a week. I simply have not spent the time to look into it. I hope that this earlier issue is not a logic board since that would not be worth fixing but I have concerns that it may be memory. It has the full 4GB installed. Also, I used Data Rescue 3 to analyze my hard drive a couple weeks ago and it was showing many spikes where they say your hard drive is getting close to failure so I had planned to put a new hard drive in in another week or so.
The reason I'm describing the earlier incident is I'm wondering if they are related. I have done a boot with the Option key pressed to get into the screen where I can choose Restore Disk. I then used disk utility and seems it found a few errors that I believe it repaired but I still have the same issue. Fortunately I have a cloned drive using SuperDuper that was done about a week ago and I use Time Machine and it had backed up about 30 mins before this incident. I am wondering if I should choose the option to restore from Time Machine. Since I did some work in the minutes before this I don't want to take that option yet.
Does anyone have any idea what's causing this and how I can repair it?