Windows 10

>>328098
If your computer came with Windows 10, use the built-in support chat and tell them you changed the motherboard because it was broken.

If you bought Windows 10, do the same, but tell them you bought windows 10, changed the motherboard and now it's not activating.

If you updated to Windows 10 from a "legitimately-activated" Windows 7, pop a spare hard disk in it, install Windows 7 on that, then run the Windows 10 media creation tool, and the Windows 10 installer. Once you update your temporary Windows 7 to Windows 10, you can put your old disk back in, and your computer will activate.

>>328098
insttall Genttoo

kmspico