Windows 7: Downgrade un-genuine version of Win7 Ultimate to valid Win7HomePremium

Hiya,
I'm really new to this forum so I would love some help.
Recently ,I bought a copy of Windows 7 Ultimate off eBay. Thinking it was real, I installed it onto my laptop which had Windows 7 Home premium.
A message now comes up saying
'This version of windows is not valid, please insert valid key'
I put on my old Windows 7 Home Premium key but a message comes up saying
'The product key you entered will not work with this edition of Windows 7. You must either run Windows 7 setup or enter a Windows 7 Ultimate product key.'
I want to revert it back to Windows 7 Home Premium (which I have a valid product key for)without losing any data.
Thanks in advance,
tristancook



PLEASE HELP ME!!!


UPDATE 25/4/11
If I edit the registry keys and then repair install is it safe or not? Do I need to make a system restore? Or is there any way that microsoft can help me.
Thanks

See here;

Startup Repair

Buying stuff like that from "unknown" vendors is always a risk.

Regards....Mike Connor

What did Ultimate provide for you that Home Premium didn't? (curious...)

You won't be able to downgrade, but instead try to do a system restore from a factory created partition, or discs you've hopefully created. Use the laptop manufacturers website and your laptop manual for details on the restore.

Unfortunately, while we can easily UPgrade within Windows 7 versions using Anytime Upgrade, MS wants us to clean reinstall if we downgrade.

However there is a popular workaround by which many beta testers switched from Ultimate to their purchased version of Windows 7. It works by tricking the installer into thinking it is doing an always-allowed same version Repair Install when it is reallly changing the version while reinstalling the OS, as a Repair Install does while keeping all programs files and settings in place.

To do this, back up your files and a Windows 7 backup image if you want a path back if needed. Then set a System Restore Point - Create, run regedit as Admin to change the two keys shown below to exactly HOMEPREMIUM for the EditionID, and Windows 7 HOMEPREMIUM for the ProductName:



Now run the Windows 7 Home Premium DVD or extracted ISO files from the desktop as shown in the Repair Install tutorial. If you need to unlock all versions in your Ultimate installer, extract the ISO using ImgBurn, run the Ei.cfg Removal Utility to unlock all version, then burn to DVD or extract or mount the ISO to run Repair Install. Be sure to select Home Premium version. Activate with the key on COA sticker.

Windows 7 Pricing Buy Install Choose Edition Features Upgrades Offers

Regards....Mike Connor