Windows Vista and Windows 7 Black Screen on Computer Unlock

Users running Windows Vista and Windows 7 might experience a Black Screen when they attempt to unlock their machine in certain conditions as follow
1. A Windows Vista or Windows 7 computer is running the "Aero" graphics mode.
2. The Windows Vista or Windows 7 computer is subject to additional security restrictions and security software, such as might be the case in the enterprise, or with mandated security settings and software such as DISA or DoD requirements.
3. The computer is locked and left undisturbed long enough for the screen to go black, which is 20 minutes with the default power policy of "Balanced".
4. A person unlocks the computer by entering their user credentials.

After the credential are entered the screen goes black, and remains black for as much as 10 minutes or longer. The machine is not "hard-locked", as periodic disk-drive activity may be noted from the disk-drive indicator light on the computer, if so equipped.

Cause:
A problem with some layer of security software causes the Desktop Window Manager to wait for an unspecified amount of time.

Resolution:
1. A temporary workaround is to Stop and Disable the "Desktop Window Manager Session Manager" service. Disabling this service will turn off the "Aero" graphics display feature, which will disable certain features such as Aero Peek, Aero Snap, Aero Shake, and so on. To disable this service:
a. Click the Start button, type "services.msc" and then press the ENTER key, or click the icon that comes up under "Programs" in the Instant Search box.
b. Locate and then double-click the Desktop Window Manager Session Manager service.
c. Locate the "Startup type" dropdown and change the value to "disabled".
d. Locate and click the button labeled "Stop".
e. Click the Apply button, and then click the OK button.

Alternatively you can run the following commands from an elevated CMD prompt to set the service properties of the Desktop Window Manager Session Manager service to not running and disabled:

net stop UxSms
sc config UxSms start= disabled

To return the settings for the Desktop Window Manager Session Manager service to normal via the CMD line:

sc config UxSms start= auto
net start UxSms

2. Updated display drivers may resolve this issue. You can determine the manufacturer of the display adapter by following these steps:

1. Click Start, and in the "Search Programs and Folder" text box, type in "MSINFO32" (without quotation marks) and press ENTER.
NOTE: The System Information tool should appear.
2. On the left-hand section called "System Summary" locate Components, and under Components locate and click on Display.
3. The right-hand section of System Information should now display information about the display system in the computer. The item called "Name" should indicate the type of display adapter.
4. At this point you can go to the Internet web site of the vendor, or the vendor of your computer to locate updated drivers.
5. In some cases you may be offered updated video drivers by running Windows Update.
6. If you are not sure of which drivers to install, contact the vendor of your computer hardware for assistance in locating an updated display driver package.

3. The final solution is to discover what layer of security software is causing the temporary blocking which renders the screen black and therefore unusable. That layer of software would need to be uninstalled or updated to prevent the blocking condition in the Desktop Window Manager.

Source:
• KB2431700