What is the computer hardware components which are essential?

Motherboard (to attach everything to)

Power Supply (for power to the machine)

Processor (must be compatible with motherboard. Computes machine code.)

heatsink (comes with processor, aftermarket coolers are available.)

Memory [RAM] (must be compatible with motherboard. DDR3 is the new standard)

Hard Drive (whether it be a solid state drive or a hard disk drive, this is what the programs and files are saved to.)

OPTIONAL

Optical drive (to install Windows OS and run CDs or DVDs)

Video Card (to boost GPU performance)

Sound card (increase and have fuller, richer sound)