There is no single cause that can be identified as the exact cause of a computer not booting up. It could be due to a number of different reasons, ranging from hardware issues, software issues, or even user-caused issues.
Hardware Issues
The most common hardware issue that can cause a computer to not boot up can be attributed to a failing power source. If the power source is faulty or malfunctioning, it will not provide enough power to the components in the machine, preventing it from booting-up successfully. Furthermore, it is also possible for the motherboard, CPU, RAM, or any other piece of hardware to be malfunctioning, thereby stopping the system from successfully completing the boot process. A failing GPU can also cause the system to not post properly if the graphics card is being used for display output during the boot process.
Software Issues
Software issues can lead to a computer not booting up if there is an issue with the operating system, BIOS, or other applications. Operating systems can become corrupt due to malware, viruses, or even user-caused errors, which can prevent it from successfully booting and running the system. An outdated or incompatible BIOS can also cause the computer to not boot correctly. Additionally, if there are programs or drivers that are not compatible or causing conflicts with the system, this can stop the computer from booting up properly.
User-Caused Issues
It is also possible that the user themselves has caused the computer to not boot up due to incorrect configurations or settings. If the user has accidentally changed a setting that prevents the computer from booting up or set the incorrect boot device order in the BIOS, then the computer will fail to boot. Additionally, problems may arise if the user tries to boot up the system with incompatible devices or drives attached, or if they have inserted the wrong disk or USB drive into the machine.
In conclusion, it is difficult to pinpoint the exact cause of a computer not booting up as there can be a multitude of different issues which can be responsible for the issue. The best way to identify the cause is to troubleshoot the machine systematically, eliminating potential causes until the exact cause of the problem can be identified.