It is recommended to proceed directly to the red part of step 3 and reinstall it.
1. Delete: rgstrtn.lck. (This file does not exist on my computer)
Type cd "%allusersprofile%\Microsoft Help", and then press ENTER,
Type attrib -h rgstrtn.lck, and then press ENTER.
Type del rgstrtn.lck, and then press ENTER.
Type dir /b /od /ad, and then press ENTER.
Type rd /q /s "<folder names>", and then press ENTER
2. Start the Windows Installer service. (This service is not started on my computer)
3. Find HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Installer\Products in the registry, delete all key values starting with 000021 (records the installation source path of Office2007)