Mac Login Logon Loop Fix
Mac fanboys say their systems never crash and never have problems. I have a love-hate relationship with my Mac, which I bought as a refurbed unit from Apple. It is a total lemon. Hard drive and motherboard needed replacement, and it is still far quirkier and less reliable than my aging Dell laptop.

The latest problem was what I call a login or logon loop. System would start as usual and get to the logon screen. I would select my user, and type the corresponding password. The computer would then go to a blue screen, and loop back to the logon screen. There are a number of web pages that hint at a solution, but these seem to be for Unix or Max OS X experts. Here is my step by step solution for the rest of us.

Turn OFF the computer. Wait a bit. Then turn it on.

While it is starting up, sometime before the "chime" (which I call a "glonnnng"), access "single user" mode by holding down CMD (Apple Key) and S

Startup will take a while and will at some point show scrolling text.

When text stops scrolling, you will see a Unix command prompt. Just to make sure, you can hit the key.

Type:

mount -uw

(this enables read write access -- you can make some BIG mistakes with all this power)

then type:

sudo -s

then type:

rm /Library/caches/com.apple.LaunchServices*

(this removes the corrupt Launch Services files)

Other useful functions when browsing around the operating system include:

ls lists directory
cd opens directory named
cd .. goes up one level in the directory structure
help gives help on a certain command
info gives more help on a certain command
users (i think this lists the users).