Jinksy is WRONG. If you have a OEM computer (say Dell, Gateway, etc.) the Windows installed is tied ONLY to that Mobo/CPU (somecases even the stupid case itself!) and will not BOOT Windows because it determines 'hey that isn't the hardware I was sold with'.
If you build a new computer you NEED a new Windows license which means a off-the-shelf Windows to install ONLY to that one PC.
Make backups of all your data then just try installing the drive, Win7 is very good at seeing the new hardware and loading default drivers for all - Win 8 isn't too bad either, if it does load itself OK, then will want to update the latest drivers and BIOS from the mobo site, run a registry cleaner (Wise has a good free one), then run Win Update, might or might not have to reactivate - and contrary to popular (mis) beliefs, this also can be done quite often with OEM copies of Windows (MS will re-activate more often than not - and they have the final say)
.... and contrary to popular (mis) beliefs, this also can be done quite often with OEM copies of Windows (MS will re-activate more often than not - and they have the final say)
Moderator: Not to argue the point, I was being specific about If a Dell Model XYZ was sold to the OP, now the OP wishes to take that drive out of that computer and put it into Homebrew ABC, both by Windows Licensing, Microsoft's Own statement (see posted many timed in the threads here) that the Windows will (and does) refuse to load because it does not, as a OEM from Dell, see Dell Modell XYZ CPU/Mobo/BIOS signature. You can't "reauthorize it" because even if you try to reload / repair the OS it won't work, as it still looks for Dell Modell XYZ Mobo/BIOS/CPu signatures before it will load.
IF he bought a generic OEM Edition of Windows (as your inferring I believe) from a reseller (similiar to what I said, Windows Off-the-Shelf) then yes your right, but most people aren't knowledgeable to know that, much less know why there is a difference between ENT edition and HOME edition.
That's why I said "quite often", the common belief, across the board is OEM copies, any and all are tied to the system it's originally installed on, which just isn't true, it's at MS's discretion to authorize or or not