A+: What Components to Check First

As the previous subsystem list indicated, there’s no shortage of places to start in virtually any subsystem. What’s the best way to decide whether a hardware, software, or firmware problem is the most likely cause? Typically, hardware problems come and go, whereas software and firmware problems are consistent. Why? A hardware problem is often the result of a damaged or loose wire or connection; when the connection is closed, the component works, but when the connection opens, the component fails. On the other hand, a software or firmware problem will cause a failure under the same circumstances every time.
Another rule of thumb that’s useful is to consider the least expensive, easiest-to-replace item first. In most cases, the power or data cable connected to a subsystem is the first place to look for problems. Whether the cable is internal or external, it is almost always the least-expensive part of the subsystem, can easily come loose, and can easily be damaged. If a cable is loose, has bent pins, or has a dry, brittle, or cracked exterior, replace it.
When new software or new hardware has been introduced to the system and a problem results immediately afterward, that change is often the most likely cause of the problem.
Hardware conflicts such as IRQ, I/O port address, DMA channel, and memory address, or conflicts between the software drivers in the operating system are typical causes of failure when new hardware is introduced. New software can also cause problems with hardware, because of incompatibilities between software and hardware or because new software has replaced drivers required by the hardware.