Hardware

These Illegal operations or freezes can, many times, be related to bad or intermittent hardware, or simply mismatched hardware. Mismatched hardware is common, even some of the large computer manufactures do insufficient analyses and testing when they select the components that make up their systems. Many components that make up a computer just don't play well together. Some modems just don't work well with specific video cards. Some sound cards are incompatible with certain main boards. The list goes on. Many manufactures only look at the cost of a given part, not its compatibility, thus they can often produce unstable computer systems.
Hardware can become defective. Mishandling the internal components of a computer can prematurely age them, which reduces their lifespan from decades to weeks or months. Many hardware failures are subtle and will not cause the computer to completely stop working, but will cause intermittent problems. Adding new internal components to a computer, especially by under-trained technicians, can cause static electricity damage to the other parts of a computer. Electro Static Discharge "ESD" is similar to when you walk across the floor touch a doorknob and receive a shock, but it's a much smaller spark. An ESD created by a person just working on the inside of a computer is so small that we can't even feel it, but it can cause great damage to the computer's internal components.

Other hardware related problems could be caused by dirty or loose internal connections, stalled or slowly turning cooling fans, improper or loose heat sinks, bad or intermittent memory, or any of a thousand other things. Please Read This, before you open your computer!