It sounds like there may be a problem with the graphics card or the motherboard. Here are some steps you can try to troubleshoot the issue:
# Check that your monitor is properly connected to your graphics card or motherboard. Make sure the cable is securely plugged in on both ends.
# Try removing and reseating the graphics card or RAM modules. Sometimes these components can come loose during transportation or storage.
# Check that the power supply is properly connected and providing enough power to all components.
# If you have an integrated graphics card, try removing the dedicated graphics card (if installed) and connecting your monitor directly to the motherboard.
# Try resetting the BIOS by removing the CMOS battery for a few minutes and then putting it back in.
If none of these steps solve the issue, it may be necessary to take the PC to a professional for further diagnosis and repair.