I am unable to log on to my other computer

Usually when I turn the computer on, you don't need to log on to a username because there is only one. On the start-up screen, however, it said "Owner" (no password). When I click on it, it says "Loading personal settings" underneath "Owner"... then it pauses. An blank error message comes up (with only the 'Yes' or 'No' option). You cannot exit the error box.
Whichever you pick (Yes or no), it continues to log on. It shows the wallpaper background then logs back off before it could load anything else.
It returns to the log-on screen. I could click "Owner"... but it would just do the same thing all over again.
Also: I've recently formatted my computer about a month ago. Everything was just fine. I've installed ZoneAlarm and something called AVG or something....
Has this ever happened before? What could I do??

Usually when I turn the computer on, you don't need to log on to a username because there is only one. On the start-up screen, however, it said "Owner" (no password). When I click on it, it says "Loading personal settings" underneath "Owner"... then it pauses. An blank error message comes up (with only the 'Yes' or 'No' option). You cannot exit the error box.
Whichever you pick (Yes or no), it continues to log on. It shows the wallpaper background then logs back off before it could load anything else.
It returns to the log-on screen. I could click "Owner"... but it would just do the same thing all over again.
Also: I've recently formatted my computer about a month ago. Everything was just fine. I've installed ZoneAlarm and something called AVG or something....
Has this ever happened before? What could I do??