Do you have explorer.exe loading somewhere like in the Startup folder or in one of the run keys of the registry?
If that is not it, then it could be in a shell command for some reason in the winlogon registry key.
Or there could be something in one of the above trying to run that is flawed and causing it.
in the winlogon key it's written "explorer.exe" corresponding to the name "shell". what should i do??