This evening my wife’s computer was being annoying. It would start up normally, display the Windows 7 splash screen, and then go completely black except for the cursor, which would move around normally. Control-Alt-Delete and Control-Shift-Escape did nothing.
Restarting in safe mode, I was able to get into the Task Manager, determine that explorer.exe was not running, and start it . So that defines the problem, but why was explorer.exe not running on startup?
A Google search pointed to a registry issue. There are a couple of keys that can (somehow) get messed up and will then keep explorer from starting. Both are in the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon folder; however, I saw one person say that he needed to do the same fix in HKEY_CURRENT_USER.
The key “shell” needs to be set to explorer.exe and the key userinit needs to be set to userinit.exe. Checking the registry, I found that shell was fine but userinit had somehow been set to “C:\Windows\system32\userinit.exe,” (with a comma at the end); resetting it to just “userinit.exe” fixed the issue.