So I have built a new computer and put all the hardware in but now I need to download an operating system. So I took the hard drive out of my laptop and plugged it into my new computer (all the plugs plugged in correctly). The motherboard notices it but says "UEFI" before the name of the hard drive. I am trying to boot off of this hard drive but it won't let me> Once I select it to boot it flashes briefly into a blue screen then restarts and ask if I want to start windows normally or launch start up repair (if I choose normally I repeats the same thing over and over). Then it searches for problems and then brings me up to an HP support interface that asks if I want to reset etc (which I don't because I want windows 7 that is on it!). Any help would be greatly appreciated.
It's simply because hardware configuration of your laptop is very different from your new pc. Windows tries to load some drivers and modules that instantly fail resulting in BSOD. In short, what you are trying to do is impossible.