I'd try safe mode and go to system restore and pick a date when you know this worked. You can also try "last known good" but I haven't found that to be very reliable.
When I turn on my computer, it loads like normal and then right before the part where I type in my password to log on, the screen stays black and all I can do is move my cursor around. I then have to turn it off by holding down the power button. How do I log back onto my user?