Well since it's not malware there was no need for a HJT Log so let's give this a try.
1. Start > Run , type in 'regedit' (without the quotes of course) in the search box .
2. Open HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon.
3. In Winlogon, on the right side, there should be a value called "Shell".
Double click this value. Make sure only "Explorer.exe" is the value of Shell, if anything else is there, simply delete it and leave 'Explorer.exe'.
Restart Windows.
PLEASE BACKUP YOUR REGISTRY BEFORE MAKING ANY CHANGES
I hope this solves the problem.
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