If I download an existing Windows 7 onto a flashdrive from an old laptop, can I use that version of Windows to download onto a custom built PC and just buy a product key from online? Thanks
Why not save yourself the trouble and buy a new Key + Installer Disk? It should only take a few days to ship to your residence if you order it online, or go out and buy it from a store. Either way, same result, same cost.
If I download an existing Windows 7 onto a flashdrive from an old laptop, can I use that version of Windows to download onto a custom built PC and just buy a product key from online? Thanks
No. This fails on multiple levels.
You need to buy a valid, legal OS for your new PC.
The OS is just as much a part of a new system as is the RAM/CPU/GPU/PSU/etc. Are you trying to cheap out on those? Hopefully not.
The license key is what actually costs. Given a valid, legal license, you can download the relevant install ISO direct from Microsoft, for free.