Use RW-Everything, select ACPI Tables and then MSDM tab this should give you your OEM product key. See here for details: [View:dellwindowsreinstallationguide.com/.../:550:0] 
Hi, my Dell Inspiron All-In-One came with Win8 preinstalled. Purchased from Staples I have the pc for about a year and was forced to do the 8.1 upgrade. The upgrade went ok but now I'm seeing a message that Windows is not activated. I call Microsoft and they said it is a volume license key and I need the retail key. I called Staples - no luck, I call Dell support, and I'm out of warrantee.  Any suggestions would be appreciated. Thanks 
Windows not activated after 8.1 upgrade