Hello, if you encounter any trouble with the steps below, please do not continue, but instead post back here.
1. Download PCRegedit_Free.ISO
2. Burn the ISO file to CD. You may need a burning toy like ISO Recorder to do this...be sure to get the version for your operating system.
3. Once you have burned this as an ISO image, insert the CD into the drive, and then restart the computer. You may have to change the boot priority in order to boot from CD. (typically the boot menu can be accessed by tapping F11 or Del)
4. Once PCRegedit is loaded, choose config, then select the file SOFTWARE.
5. Navigate to root > Microsoft > Windows NT > CurrentVersion > Winlogon.
6. Look for the Shell
value and make sure that the value is set to explorer.exe Most likely the Shell value data will now look like: C:\Windows\Temp\<some random name>\setup.exe
Exit and save the changes if asked, reboot in Windows and see if you still get the error.