First thing I’d say is have you checked you POWER SUPPLIES !
You swithc on you PC and discover that all is not well. You will have one of two basic problems:

The PC appears to be dead, i.e. the monitor is blank.
The PC won’t boot up, i.e. it starts but then stops before completion.

Starting with the first scenario- a PC with no obvious signs of life.

When this happens the first thing to you need to do is establish whether you have power available to your PC. A basic principle that applies to all electronic or electrical equipment, not just computers, and in this case is easily established by observation.

Check if all the LEDs (lights) on the system case lit and the power supply fan blowing?

Do you see any lights on your keyboard?

If you find that the the answer to any of these questions is yes, then the systems power supply is operational.

The problem is if the answer is no, then check the following:

Is there power at the wall socket? How do you check this ? Very simple plug another appliance into it, if that works then the socket is OK. Remember, the computer power cables are usually the same type used with electric kettles and some other household appliances. This makes it a simple task to check them by substitution.

Are you using a surge suppressor or some similar device? If so, try removing or bypassing it and see if that cures the problem.

Next, check the PC’s power cable. Try substituting it with your electric kettle cable, these are usually the same type.

Most PCs also have an on/off switch at the rear of the case. Check that this isn’t in the off position.

If none of these is causing the problem then the PC’s power supply unit is defective and this calls for replacing the defective pieces.

However, if your power supply id functioning, then you have one of three potential problems. Either the monitor, the motherboard or the graphics system is faulty.

Absolutely first thing to check when your PC appears to be ‘dead’ is the power supply. Don’t forget to check the external (mains) power supply as well.

The easiest way to establish that your power supply unit is operational is to check that the fan is working and that the keyboard lights are one.