The computer hardware contains a lot of electronic circuits, without the proper software, the hardware will stay just that, a heap of interconnected electronic components. The first task the OS does is to load itself into the main memory, and run itself, a feat comparable to pulling yourself up with your bootstraps, the term 'booting' derives from just that metaphor. At 'boot time' the computer is still just a component's heap, there is yet no friendly OS that can load and run programs with a single call to a system routine. The magic is performed in several stages, each loading a larger functional subset of the OS, and each doing the preparations needed for the next stage.
Halted mode is the right mode to switch off power.
The operating system may put the processor in that mode when a serious internal error occurred. The best way is to read carefully the appropriate guide, and get as much advice as possible from the company's technicians. No OS is useful if you can't use it, and the better you know it, the more it will be useful. Put another way, you should learn how to use your operating system, read the online help, user manuals etc. Unfortunately, this is a long-standing problem which is particularly acute for graphics functions.