There is a big difference between your computer does not turn on and your computer is on but don’t see anything on your screen. If your computer does not turn on at all then you should NOT be hearing the fan or any noises coming from it. There should be no lights at all on it, and when you hit the caps lock key on your keyboard it should NOT light up. In this situation you should try the following items in order.
Confirm All Cables are Plugged In
1. Do an external check on your PC-This may seem obvious but confirm the power cord is in a good, working electrical socket. Also confirm that the cord is plugged into the power supply very tightly.
2. Check your monitor cable-This sounds obvious but make sure you see a light on the power button on your monitor if this is not a laptop. Also check the power cable and your video cable to make sure they are firmly plugged in.
3. Is there any sound coming from the PC? After you check the above items confirm that when you hit the power button that the computer stays completely silent. If this is the case then your computer is not getting any power. This all points to a failed power supply on your computer. If your fan is running and nothing is on your screen then it is not your power supply. Check this post on our blog for a possible failed hard drive.