Try the link below - this was done using google.com using the words "Windows Installer is not correctly installed" - results were achieved in less than 10 seconds!!!! (keep it in mind for future problems)
Hope they help
Some of my apps refuse to install because of an error saying "The Windows Installer Service could not be accessed. This can occur if you are running Windows in Safe Mode, or the Windows Installer is not correctly installed."
Is there any way to resolve this?