Recently encountered problems getting Windows Explorer shell to load in Windows XP after cleaning a spyware infection. I found there are two registry keys that are critical in relation to loading explorer on boot, you should check them first if you even encounter a problem getting Explorer.exe to load.
HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionWinlogon
shell=”explorer.exe”
HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionWinlogon
userinit=C:windowssystem32userinit.exe
Watch out for trailing comma’s on userinit.exe (userinit.exe, ) as this is where malware likes to insert itself to load during windows startup.