Want to use old SSD drive that currently has windows 8.1 as OS drive in new build that will have windows 10.

[gridlock332]

I'm upgrading my old computer's Mobo, CPU, GPU, and RAM. I also want to install windows 10 on the new build (I have a new copy of windows 10). I want to use the old SSD in the new build but it currently has windows 8.1 installed on it and it's running my computer. What do I have to do to use it in the new system? Can I just plug it into the new Mobo, throw in the windows 10 boot CD and it will work? Or do I have to uninstall the old windows 8.1 before I plug it into the new Mobo and try installing windows 10?

 

[jojesa]

Yes, you could just connect the SSD and select “Custom” option to perform a clean install. Delete all partitions on the SSD and let Windows 10 install itself in the unallocated space. Make sure to backup any files you want since the disk will be wiped clean.
During setup, if you see the activate Windows 10 select “I don’t have a product key”. Windows 10 will automatically activate after it’s installed (you will be ask to enter the license key).

I would suggest installing the latest Windows 10 version available from Microsoft website...by creating an installation media.

Also you could have updated the old system to Windows 10, create a Microsoft account and link it to your license. Use that license to install Windows 10 on the new system.