If your Windows 7 or Vista explorer.exe fails to start up automatically on every boot, here are a few steps you may wish to carry out:

1) Please see if it starts in safe mode. If it does then obviously something is interfering with its normal start in regular mode.

2) I suggest you scan for malware in safe mode, remove infections if any and reboot.

3) See if a System Restore helps you.

4) Open regedit and navigate to :

HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon

In the RHS Pane, ensure that the default string value of : “Shell”=”Explorer.exe”.

Exit.

5) Start >Search Menu Bar > Run cmd as admin > sfc /scannow .

Hope something helps.