First, it seems that different reason can cause this problem. My solution may not work for you.

Symptom:
1.Black screen after the green progress bar, before Vista Logo.
2.Mouse can move.
3.Ctrl+Alt+Del doesn't work.

Solution:
1.Reboot the machine
2.Keep hitting F8.
3.Choose 'Repair your computer'. 'Last know good' didn't work for me.
4.The first choice should be repair boot process or something the like. I tried. It found nothing.
5.Then I tried the second one, which should be system recovery or something the like. The one guarantee your documents will not get touched. I restored to something a couple days ago. It works good for me.

Root Cause:
I guess the reason is related to multi-account. I was trying to access files in another user's folder when I was in my account. Then windows gave some error message and tried to restart. When I restart, I got the problem.