Office is installing in the background (84%) stuck there.

Also I have noticed that although the Office programs seem to work if you go into the individual programs and open files using their "Open" buttons, Office file extensions are not automatically associated with Office applications, so to double-click a Word doc or Excel spreadsheet in Windows Explorer won't launch the appropriate program.  If I try to use the default program feature in the Control Panel, it hangs on loading file types.

This issue is driving me mad - has no one found a solution yet?

Nope. Have tried both the 64 and 32 bit versions of the Office 2013 MSI installer, and even tried installing on a different hard drive. It installs to a certain point (84% most likely, MSI install doesn't give a percentage #), hits a problem, and uninstalls itself. Nothing works, not even a complete reinstall of Windows 8. I'm surprised Microsoft hasn't fixed this or even owned up to the problem yet. Wait, no I'm not. Their customer service is terrible.

The issue is caused because NETWORK SERVICES (NS) lacks disk read write permission. I coppied the tmp msi installer from \windows\installers and ran it and got an error code. Went to \Program files\common files\Microsoft Shared\OfficeSoftwareProtectionPlatform
and gave NS permission. The on line installer installed Office but at 94%. Expect it a similar problem.

By the time I tried all the various ideas I found on search engines, etc., I had my computer so bunged up it wasn't funny....and I'm not an amateur with computers.  I ended up copying all important data onto an external hard drive and then completely restoring my computer to its factory default state.  I applied all critical Windows Updates and then proceeded to install Office 365 before installing anything else.  It installed without a problem and is working just fine.  I'm now in the process of reinstalling all of my other programs and restoring my data.  Man, what a pain!  But, I'm almost done......