Windows Installer Service could not be accessed

[This is for Windows XP]

I encountered this problem while installing MS .Net Framework 3.5 Sp1. It failed with an error code MSI 1601, which is "The Windows Installer Service could not be accessed. Contact your support personnel to verify that the Windows Installer service is properly registered." according to http://support.microsoft.com/kb/229683. Interestingly, I was unable to uninstall any programs which uses Windows Installer from Control Panel's Add/Remove Program as well! 

Well, there are a few troubleshooting steps you can take, before you start panicking =).

1. Run Services.msc in Start->Run. Scroll down until you find Windows Installer. Try to start it if you can find it. If you can't find it, see the next step. If you're unable to start it, go to step 3. 

2. If you can't find Windows Installer, Run CMD in your Run Command to open the Command Prompt. Run the following lines to reregister the service without the qoutes:

"msiexec /unreigster"

"msiexec /regserver"

If it still doesn't appear in your services. you will need to reinstall Windows Installer. It can be downloaded from http://www.microsoft.com/downloadS/details.aspx?familyid=5A58B56F-60B6-4412-95B9-54D056D6F9F4&displaylang=en. 

3. In the rare cases that you're unable to start the service, this is usually due to the installation of the AppLocale Utility (which happened to me).

One way to fix this is to delete the following key regedit: "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Custom\MSIEXEC.EXE". Remember to do a backup of your registry before you delete the key.

If the steps above did not help you, please refer to the KB at http://support.microsoft.com/kb/315346