What to check when computer is not booting.

When troubleshooting a computer that isn't booting, there are several steps you can take to diagnose and potentially resolve the issue:

1. Power Supply: Ensure that the power cable is securely connected to the computer and the power outlet. Check if the power supply unit (PSU) switch is turned on, and listen for any sounds indicating the PSU is functioning (e.g., fan noise).

2. Hardware Connections: Verify that all internal hardware components (CPU, RAM, GPU, hard drives, etc.) are properly connected to the motherboard. Sometimes, loose connections can prevent the system from booting.

3. Display: Check if the monitor is turned on and properly connected to the computer. Test the monitor with another device to ensure it's functioning correctly.

4. Peripherals: Disconnect all unnecessary peripherals (e.g., external drives, printers, USB devices) from the computer and see if it boots without them. Faulty peripherals can sometimes cause booting issues.

5. BIOS/UEFI Settings: Access the BIOS/UEFI setup utility (usually by pressing a key like Del, F2, or F10 during startup) and ensure that the boot order is correctly configured to prioritize the boot device (e.g., hard drive or SSD) where the operating system is installed.

6. Boot Device: Try booting from a different device (e.g., a bootable USB drive or a live CD/DVD) to check if the problem lies with the boot drive or the operating system.

7. RAM: Remove and reseat the RAM modules. If you have multiple RAM modules, try booting with each one individually to identify if any of them are faulty.

8. CPU: Ensure that the CPU is seated properly in its socket. Check for any bent pins on the CPU socket.

9. Graphics Card: If you have a dedicated graphics card, ensure it is properly seated in its slot. If you have an integrated GPU, try removing any dedicated graphics card and booting with the integrated GPU.

10. Power On Self Test (POST) Beeps: Listen for any beep codes during startup. These can indicate hardware issues. Consult your motherboard's manual for the meaning of different beep codes.

11. CMOS Battery: If your computer's BIOS settings are getting reset every time you power on the system, it could indicate a failing CMOS battery. Try replacing the CMOS battery.

12. Faulty Components: If none of the above steps resolve the issue, it's possible that a hardware component (e.g., motherboard, CPU, PSU) is faulty and needs to be replaced. Troubleshooting individual components may require professional assistance or specialized diagnostic tools.

By systematically checking these components and connections, you can often identify the cause of the booting issue and take appropriate action to resolve it.