Have you tried cleaning out your Temp folder, you can do it by typing %temp% in the Start Menu RUN box. This will open your Temp folder, there you can delete everything that Windows will allow you to do so.
It may be necessary to show Both Hidden and System Files, and also to uncheck "Hide known file types" in Control Panel/ Folder Options/ View, to navigate to the mentioned Temp location.
You can look at the Google Earth Forums for assistance or at the following links:
One states to use the Windows Installer Cleanup Utility which is no longer available as it was found to damage some Windows components. Do a search for software removal tools to removall all instances of Google Earth. Then download the latest version which
I believe is 6.0 and try the installation again.