you turn on your desktop computer. You can hear the fans start up, but the monitor remains blank. You wait a while, but it doesn't appear that anything else is happening. The hard drive activity light doesn't show activity, and you never hear the sound that plays when Windows loads.Which of the following are the most likely cause of the problem?

If you turn on your desktop computer and the monitor remains blank, the problem might either be as a result of Processor not working, Video card bad and memory not sitting well.

if the problem is associated with processor, do the following:

Check if the power LED light on the motherboard is on or off.

If the LED light is off, check for motherboard or power supply issues.

If the LED light is on, check if the processor fan spins when the system is powered on.

Another major cause could be that the Video card is bad first thing to do is Update the drivers, then reseat the Videocard or probably change it.

Lastly memory module is loose, the computer might not display an image. In other words, your computer starts but the screen is black.

Now, you can try resetting the memory modules to fix the "PC turns on but no display" issue. Remove memory module from the memory slot, and then put it back into the slot to get a better connection so that the computer can recognise the memory.