How to fix the "The Windows Installer Service Could Not Be Accessed" error in Windows XP

When you try to install a program, such as Microsoft Office or even try to remove an installed program for Windows XP, you may receive the following error message:

"The Windows Installer Service could not be accessed.This can occur if you are running Windows in safemode, or if the Windows Installer is not correctlyinstalled. Contact your support personnel for assistance."

To resolve this issue, follow these steps:
1. Log on to your computer as an administrator.
2. Click Start, and then click Run.
3. In the Open box, type cmd, and then click OK.
4. At the command prompt, typemsiexec.exe /unregister, and then press ENTER.
5. Type msiexec /regserver, and then press ENTER.
6. Verify that the SYSTEM account has full control access permissions to the HKEY_CLASSES_ROOT hive in the Windows registry. In some cases, you may also have to add Administrator accounts. To do so:Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 (http://support.microsoft.com/kb/322756/ ) How to back up and restore the registry in Windows
a. Click Start, click Run, type regedit in the Open box, and then click OK.
b. Click the following registry hive:
HKEY_CLASSES_ROOT
c. On the Edit menu, click Permissions.
d. If SYSTEM is not listed in the Group or user names list, click Add, make sure that the local computer name appears in the From this location box, type system in the Enter the object names to select box, click Check Names, and then click OK.
e. Click SYSTEM in the Group or user names list, and then select the Full Control check box under Allow in the Permissions for SYSTEM box.
f. Click Apply, click OK, and then quit Registry Editor.

7. Restart the computer. If the problem is not resolved, repair Windows XP. For more information about how to repair Windows XP, click the following article number to view the article in the Microsoft Knowledge Base:
315341 (http://support.microsoft.com/kb/315341/ ) How to perform an in-place upgrade (reinstallation) of Windows XP.