There are many possible explanations for why your computer is not booting up. If you have already gone through the basic steps such as checking the power cables, resetting the BIOS and ensuring that all hardware components are correctly connected, the following may help you narrow down the issue:
1) Check the Power Supply Unit (PSU): Is it supplying enough power to your system? To test this, try using a different power cable and/or power supply and then see if your computer boots up. If the PSU fails to provide enough power, the motherboard or other components may not get enough power to start.
2) Check the Motherboard: The motherboard is responsible for powering all components in the PC, as well as connecting them together. Check for any signs of damage such as burnt components or broken connections. You can also check the BIOS settings before proceeding further.
3) Check the RAM: RAM (Random Access Memory) is the main source of temporary storage for your system. If RAM is faulty or not installed correctly, the computer may not boot up properly. Check for any loose connections or try replacing the RAM with a known working module.
4) Check the Hard Drive: The hard drive stores all your data and programs, including the operating system. Try removing it from the system and testing it on another computer. If it works fine, then the problem is likely caused by an issue with the software installed on your machine.
5) Check the Graphics Card: The graphics card is responsible for displaying visuals on your monitor or TV. Check that it is properly seated in the slot and there are no visible signs of damage. If the issue persists, try replacing the card with another one.
6) Check the Power Button: The power button is responsible for controlling the flow of electricity to your computer. Check that it is not stuck or damaged. If the issue persists, try replacing the button.
7) Check the Operating System: If you are sure that all the hardware components are working, the issue might be caused by the operating system. Try reinstalling the OS or restoring the system to its original state.
8) Check for Viruses: Viruses and other malicious software can interfere with the way your computer operates. Make sure to run a full scan of your system with a reliable antivirus program.
If none of these solutions work, you may need to enlist the help of a professional. A qualified repair technician may be able to identify the source of the problem and fix it for you.