When you attempt to install a program that uses Windows Installer, such as Office XP, you receive:
The Windows Installer service could not be accessed. This can occur if you are running in safe mode or if the Windows Installer is not correctly installed.
This error is probably the result of a damaged registration service.
To resolve this issue:
1. Open a CMD.EXE prompt.
2. Type msiexec /unregister and press Enter.
3. Type msiexec /regserver and press Enter.
NOTE: See Overview of the Windows Installer Technology.
NOTE: See MSDN's Overview of Windows Installer.