If every time your Windows computer starts, your explorer does not start and you are left seeing the wallpaper only, and you are left with no choice, but to start explorer.exe manually, then here are a few troubleshooting steps you may want to try.
1. Scan your computer with an antivirus and anti-spyware.
2. See if you can login in safe mode. That way you will then know if its any program which is interfering with your explorer.exe.
2. Open regedit and navigate to :
HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Here ensure that the subkey Shell, in the right pane has value explorer.exe
Also ensure that the value of AutoRestartShell in right pane is ‘1‘ (Hexadecimal). This determines whether the explorer.exe is re-started automatically if it stops unexpectedly. Exit regedit.
3. In start search, type sfc /scannow . In the search result, right click and Run As Administrator. The scan will replace corrupted system files, if any. Reboot when asked.
4. See if a System Restore helps you.
Hope something does! 
Source: windowsclub
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