PC troubleshooting efforts could be focused to areas such as power supply, video, mother board, CPU and the hard drive. If there is a failure in any one of these systems the computer will not work. It is your job to play detective and determine which of these systems have failed.
First I would start by making sure that the power supply is operating. You should never ignore the potential of a failed AC power supply or even something as simple as a disconnected power cord. I recommend disconnecting the power supply to the mother board and testing for power from the power supply to make sure that you are getting the right amount of electricity to the motherboard. Quite often you will find that power supply units do not last as long as the computer.
In terms of troubleshooting video failures we usually mean no image at all on the screen. Simple cases which could be diagnosed are such where the monitor or LCD screen is failing to power up properly, or the PC failing to power up at all. Video card failure is not a rare occurrence, and video boards could loose contact with the motherboard socket. Video failure could be due to motherboard failure or the result of some external interference if the symptom is poor image quality.
Failure of the motherboard often shows up as second level problems. A motherboard problem could often be an issue with any of the circuits that connects to any component of the mother board. This type of problem is best fixed with a different motherboard. It is more economical to have a replacement motherboard on hand as opposed to attempting to repair the motherboard itself. To repair one requires special tools and training.
If you have a boot error that points to the CPU you could try the unit in another machine to see if the error follows the CPU. If you intend to troubleshoot computers it is very good to have extra spare parts on hand. This gives you the freedom to swap and try different parts in order to determine to root cause of the failure.
Hard drive failures are typically simple to troubleshoot, partially because the operating system includes tools to report on the hard drive reliability when it’s accessible. There are also tools on the market that will help you fix most hard drive problems.
PC troubleshooting requires a systematic approach and is easy to do. Some of the worst symptoms are caused by computers that will not boot, display scary and/or confusing error messages. Computer hardware problems are typically the simplest types of problems to solve.