Motherboard Activation
When you have a motherboard replaced, you sometimes get the message that you have to re-activate windows. There is two causes for this.
First Cause
Microsoft has installed a means to make sure the software is not pirated. If windows detects numerous changes in the hardware, it will require the owner to call Microsoft and explain why. Most of the time, the owner calls Microsoft and will give the owner a code to enter to resolve the issue. If you have made changes in your system, give Microsoft a call to get it reactivated.
Second cause
Dell uses Service Tags to identify their systems. On older systems it was a series of five numbers and letters. The newer systems use 7 numbers and letters. When you go into the bios you can see the service tag listed there. When a motherboard is replaced, the technician is suppose to make sure the service tag is entered in the bios. If this field is left blank, Windows can require the owner to re-activate but the system will not re-activate until this field is filled in. If this field is blank, call Dell to have it resolved.