Symptom
In some cases, you may not be able to shut down or restart your PC after using Safe Exam Browser (SEB), and Ctrl-Alt-Del does not show the Task Manager either.
Cause
While running, SEB changes Windows Registry settings for the options in the Windows Security Screen invoked by Ctrl-Alt-Del. These Registry settings are nor properly reset to the original values in case
your PC would be force reset while SEB is running, or
SEB has crashed.
Solution
Run the following tool in your Program Files directory: SafeExamBrowser\SebWindowsServiceWCF\SebRegistryResetter.exe
This will result in the Registry settings being properly reset, and you will be able to shut down or restart your PC again.