Facing a situation where your computer won't boot up can be distressing, but there are several steps you can take to troubleshoot and potentially resolve the issue. Here's a comprehensive guide:

• Check Power Supply:
    Ensure that the power cables are securely connected to both the computer and the power outlet. Test the power outlet with another device to confirm it's functional. If you're using a power strip, try connecting the computer directly to the outlet.
• Inspect External Connections:
    Disconnect all external devices such as USB drives, printers, or external hard drives. Faulty peripherals can sometimes interfere with the boot process.
• Perform a Hard Reset:
    Power off the computer, disconnect the power source, and hold down the power button for 15-20 seconds. Reconnect the power and attempt to restart. This helps discharge any residual power and can resolve certain startup issues.
• Check Display Connections:
    Ensure that the monitor is properly connected and powered on. If you have multiple displays, confirm that the correct input source is selected. A faulty display connection might give the impression that the computer is not booting.
• Boot in Safe Mode:
    Attempt to boot the computer in Safe Mode. Safe Mode loads the system with minimal drivers and can help identify if a third-party driver or software is causing the boot failure.
• Use System Repair/Recovery Options:
    On Windows, you can access System Repair or Recovery options by booting from a Windows installation or recovery disk. These options provide tools to repair startup issues, restore the system, or access advanced troubleshooting features.
• Check for Disk Errors:
    Boot from a system repair or installation disk and utilize tools like CHKDSK (Check Disk) to scan and repair potential disk errors that might be preventing normal booting.
• Access BIOS/UEFI Settings:
    Enter the computer's BIOS or UEFI settings during startup. Verify that the boot order is configured correctly, with the internal hard drive or SSD as the primary boot device. Incorrect boot priorities can lead to startup failures.
• Perform a System Restore:
    If the computer was functioning correctly in the past, consider using System Restore (Windows) or Time Machine (Mac) to revert your system to a previous state.
• Use Bootable Media:
     Create or use a bootable USB or DVD with a system repair or installation tool. This provides access to additional diagnostic and repair tools.
• Check for Hardware Issues:
     Inspect internal components such as RAM, hard drive, and graphics card for loose connections or damage. Reseat components if necessary, and consider testing with spare parts if available.
• Reinstall Operating System:
     If all else fails and you have critical data backed up, reinstalling the operating system may be an option. This should be a last resort, as it wipes all data on the system drive.
• Seek Professional Assistance:
     If you are unable to identify or resolve the issue, consider seeking professional help. Contact the computer manufacturer's support or consult with a certified technician for further diagnosis and repair.

By following these systematic steps, you increase the chances of identifying and resolving the issue preventing your computer from booting up. If problems persist, professional assistance may be the most effective course of action.