Based on the troubleshooting steps you've already taken, it seems like you've covered many of the common causes of a no display issue. Since you've already reset the BIOS, changed the RAM, power supply, and processor, here are a few more suggestions that you can try:
1. Check the Graphics Card: If you have a dedicated graphics card installed, try reseating it in the PCIe slot or using a different PCIe slot if available. If you're using integrated graphics, try installing a dedicated graphics card to see if the issue is with the onboard graphics.
2. Check the Monitor and Cables: Ensure that the monitor is properly connected to the computer and that the cables are in good condition. Try using a different monitor or connecting the current monitor to another device to rule out monitor issues.
3. Inspect the Motherboard: Check the motherboard for any visible signs of damage such as blown capacitors or burnt areas. Ensure that all power connectors are securely plugged in.
4. Test with Minimal Hardware: Disconnect all unnecessary peripherals such as extra hard drives, optical drives, and expansion cards. Leave only the essential components connected (CPU, RAM, graphics card) and see if the system boots up.
5. Test with a Different Power Outlet: Plug the computer into a different power outlet to rule out issues with the power source.
6. Check for Overheating: Make sure that the CPU cooler is properly installed and that the CPU is not overheating. You can check this by monitoring the temperature in the BIOS or using software tools.
If after trying these additional steps the issue persists, it could indicate a more complex hardware problem such as a faulty motherboard or CPU socket. In such cases, it might be beneficial to have the system checked by a professional technician for further diagnosis and repair.