Using an existing operating system in a fresh installation Recycling an OS during a new setup
Using an existing operating system in a fresh installation Recycling an OS during a new setup
Usually you don't need to reinstall unless it's required by the system. Sometimes it happens on Windows, and it may warn about significant changes in hardware. It could be unnecessary.
Make sure you keep the activation code safe. Useful guide from How To Geek on locating product keys is available at the provided link. Note that those stating it won't work with an OEM key are misunderstanding the situation.
For retail versions, you might need to re-enter the product key. With OEM copies, you can either contact MS to get the key back or purchase a fresh one.
Online shops provide limited retail options. Visit http://pcpartpicker.com to discover nearby stores. If none are available, purchase directly from Microsoft.