replaced motherboard - now get 'Windows is not genuine'

The Dell OEM OS is designed to run on a Dell motherboard (BIOS).  Usually it won't even install on a non-Dell M/B.

Legally, the Dell OEM OS is only licensed for the PC it was delivered with.  As you have replaced the motherboard with a non-Dell M/B it not longer is a "Dell".

When you buy Windows pre-installed by an OEM, you are purchasing it at a significant discount; part of the price you pay for that discount is that limitation.  You can, however, legally (as per the license) replace the motherboard with a validated motherboard for that system without voiding your license.  A Retail license can be moved to another system, but the cost is significantly higher than an OEM license.

thanks..

but pfui on that for an idea, the Dell MB gives up the ghost and there goes Windows too ? bah. oh well, finally time to upgrade to Unbuntu..

"You can, however, legally (as per the license) replace the motherboard with a validated motherboard for that system without voiding your license."

For example Dimension 8200 to 8300, or even 8300 to 8400?

The boards appear to physically be interchangeable,  I could be wrong.

I will try to answer it myself.  

Windows activation is based on changes to:          DIM 8200 > 8300         DIM8300 > 8400

• Display adapter                                                   (unchanged)                        NEW
  
• SCSI Adapter                                                            ------                                   ------
  
• IDE adapter                                                               NEW                               NEW
  
• Network adapter MAC address                              NEW                               NEW
  
• RAM amount range (e.g. 0-512 MB)                 (unchanged)                     (unchanged)
  Processor type and serial number                     (unchanged at first)            NEW
• Hard drive device and volume serial number    (unchanged)                   (unchanged)
  Optical drive (e.g. DVD-ROM)                            (unchanged)                   (unchanged)
  

Whether the board is a Dell or not must be an additional factor for a Dell OEM Windows activation acceptance.

My opinion is that changing all 4 at once even if still a Dell would be too much. 

Would the OEM Windows be valid for a Dell system upgrade?

What do you mean by "Dell system upgrade"?

I'm not sure I entirely understand your table either or what it represents.

Technically the license is void if you don't replace the motherboard with an accepted or validated motherboard model (which would return Manufacturer=Dell and Model=DIM8400 for a BIOS query) for that model.  For example, there might be 4 part numbers for motherboards for a Dimension 8400, any of which will be programmed to correctly respond to BIOS queries, where an 8300 would not.  Also, the license is dead if you replace the board with a non-Dell, as well.

"I see Windows XP Dell OEM Reinstallation disks on eBay as "New Windows XP Home" often still sealed, but of course no warnings at all  that it is only for Dells and only narrowly usuable then."

That comes with the territory and is a pretty well-known caveat to using OEM software ... one must understand the reason and situation for needing a Dell reinstallation disk.

My table compares what is different for both upgrades based on Windows Activation besides the motherboard code.   A Dimension 8400 upgrade would require reactivation even with a retail license.

My question looks to be answered by the statement that the system looks for the specific mobo codes for a Dimension 8300 to allow the use of the Product Key on the Dimension 8300 case.

I asked the question because of an apparently dead motherboard in my Dim.8300 and an interest in replacing it with a PCI-E board such as the Dimension 8400.

Buyer beware:

I see Windows XP Dell OEM Reinstallation disks on eBay as "New Windows XP Home" often still sealed, but of course no warnings at all  that it is only for Dells and only narrowly usuable then.