After loading the HKEY_CURRENT_USER Registry hive from this user account, it's finally time to load the Windows shell. This process begins by loading any executables listed at HKLM\SOFTWARE\Microsoft\Windows NT\ CurrentVersion\Winlogon\UserInit, which by default points to '\Windows\System32\UserInit.exe'.
The UserInit program runs any log-on scripts named in HKCU\Software\Policies\Microsoft\Windows\System\ Scripts, and the equivalent HKLM Registry key. It finally locates the program stored in HKCU\SOFTWARE\ Microsoft\Windows NT\CurrentVersion\Winlogon\Shell (or the HKLM equivalent if that doesn't exist), which by default is 'explorer.exe'. The desktop is initialised, the taskbar appears, startup programs are launched and you're finally able to use the PC. At least, that's what should happen.
Boot problems here may be caused by missing or corrupt data. There may be a problem with the Registry hive for your user account, for instance. If the Registry pointers to 'UserInit.exe' or explorer.exe are missing then the boot won't complete. Use System Restore or use the Last Known Good Configuration to fix the problem.
The most likely issues arise from thirdparty conflicts, though, either apps you've installed or malware that's infected your PC. In extreme cases the Windows desktop won't appear correctly and you'll receive an error message saying that explorer.exe 'failed to initialise properly'.
You may be able to work around an explorer.exe initialisation problem by closing and relaunching the current process. That is, press [CTRL]+[Shift]+[ESC] to launch Task Manager, select the Processes tab, right-click 'explorer.exe' and select 'End Process Tree'. Then click 'File | New Task', type 'explorer.exe' and press [Enter].
If that fails, try booting into Safe Mode, use System Restore or boot from the Last Known Good Configuration. If you've just installed something that might have caused the problem, remove it. Otherwise, see the 'Startup Troubleshooting' box for tools that should soon have your system running smoothly again.
First published in PC Plus issue 275