With the latest updates that are being sent down the update pipe many users are facing new problems after the restart.
A computer that loads straight to desktop will present with a user icon to login with.
When you click this icon one of two things happens,
A) Your presented with the welcome screen and then a black screen then the moniter shuts off for a second and then you are represented with the login screen.
B) the former happens but when the screen goes black your cursor is present in the middle and nothing else happens.
When condition B happens you can use cntrl alt del and restart explorer.exe
From here check to see if you have restore points, it seems that only 10% of the people experiencing this bug have them.
If this does not work you can restart in safemode with networking.
If no restore points are present open an elevated cmd prompt.
Start>All Programs> accessories> right click cmd and select run as administrator
Enter the following into the cmd prompt
This bug is fairly new and microsoft isnt sure whats causing it, majority of the people online are calling it the black screen error.
Alot of people will tell you a repair install is nescessary and i found this after digging through 20 pages of google results and it worked for me and several other so you might give this a try before you have to go through the hassle of setting your pc back up.