Products: Windows NT Family (2000, XP, Server 2003...)

Symptoms
By default, Windows Installer cannot be accessed in safe mode. Something of the following nature could occur when tried to access: 

Solutions

• To enable Windows Installer from a Command Line:
  - Start >> Run >> cmd. Enter the following:
  
  REG ADD "HKLM\SYSTEM\CurrentControlSet\Control\SafeBoot\Minimal\MSIServer" /VE /T REG_SZ /F /D "Service".
  
  You will get the result, "The operation completed successfully".

• To enable Windows Installer from Computer Management:
  - Start  >> Run >> compmgmt.msc (OR right click on "My Computer" and "Manage")
  - Expand "Services and Applications". Go to "Services". Locate and Select "Windows Installer" in the Name Field.
  - Go to "Action" and hit "Start" (OR there will be a 'play' button in the tool row, click on it).
  
  

More Info
How to start Windows in Safe Mode?
Restart the computer and Press F8 before the boot menu or splash screen.