Zune 4.7 does not uninstall / Zune 4.8 does not install

I'm trying to update my Zune software to the latest version.

Trying to update the Zune 4.7 software fails in the following ways:

FAILURE 1

1. Run Zune (4.7.1404.0)
2. Settings -> General -> Check For Updates
3. Dialog appears, "Your Zune software is already up to date."

FAILURE 2

1. Run Zune
2. Connect Windows Phone 7.5 (7.10.7720.68 on an HTC HD7)
3. Dialog appears, "PHONE IS LOCKED - To sync media using the Zune software, first unlock the phone using your PIN."
4. Unlock Phone
5. Dialog appears, "ZUNE SOFTWARE UPDATE IS REQUIRED - To continue, Zune needs an update. To get the update, click OK."
6. Click OK
7. Accept UAC prompt
8. Dialog appears, "Downloading updates..."
9. Dialog changes, "The latest version of Zune software is already installed on this computer. No update is available."

FAILURE 3

1. Control Panel -> Uninstall a Program -> Zune -> Uninstall
2. Dialog appears, "ARE YOU SURE YOU WANT TO UNINSTALL ZUNE? - ..."
3. Click YES
4. Dialog changes, "UNINSTALLING THE ZUNE SOFTWARE..."
5. Dialog changes, "UNINSTALLATION COMPLETE - The Zune software has been removed from this computer."
6. Click CLOSE
7. Now note, not one thing appears to have actually been uninstalled. Desktop icon still exists, C:\Program Files\Zune is still fully populated, and it still exists in the Control Panel's list of applications which can be uninstalled (attempting to uninstall it again merely loops back to step 1 of this process). In fact, if you click on the desktop icon, Zune opens as if it had been freshly re-installed with the intro video and setup prompt.

FAILURES 4 & 5

• Attempting to use the latest version of UnZoone (1.3.3) only removes the desktop icon as far as I can tell, Zune 4.7 still runs from the EXE in Program Files.
• Perfect Uninstaller - removes some to all registry keys, and some to all of the files, however the system still isn't in a clean enough state to install Zune 4.8 (see errors below)

FAILURE 6

1. Do all of the above to uninstall to the best of my ability
2. Download Zune Software 4.8 from http://www.microsoft.com/download/en/details.aspx?id=27163
3. Run ZunePackage.exe (270 MB, 4.8.2345.0)
4. Accept the UAC prompt
5. Installation frozen at 0% indefinitely. "PREPARING YOUR COMPUTER" is greyed out, as is "INSTALLING THE ZUNE SOFTWARE".

FAILURE 7

1. Do all of the above to uninstall to the best of my ability
2. Download Zune Software 4.8 from http://www.zune.net/en-ww/downloadsoftware.htm
3. Run ZuneSetupPkg.exe (100 MB, 4.8.2345.0)
4. Accept the UAC prompt
5. Dialog appears, "CHECKING FOR UPDATES..."
6. Update check frozen at 0% indefinitely.

* Restarting at every possible location does not solve the problem

If I attempt to reinstall Zune 4.7 from a file I found online (ZunePackage47.exe, 246 MB, 4.7.1404.1), the installation is successful, but results in an installation that still cannot be updated.

Any suggestions before wiping my hard drive and starting from scratch?

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Here's a post on another forum where someone has nearly the same problem. Their solution was "to wait for the next version of Zune to be released" and hope that works. A very undesired option for me.

http://www.zuneboards.com/forums/showthread.php?t=47465