If you try to turn on the computer and it doesn't answer, the first thing to do is look at what symptoms are showing: either press the button and do nothing, or turn the lights and fans on and off for a while. It may also be generally open but may not show the image on the screen.
Let's take a look at what they should do in each case.
If the computer does nothing by pressing the power button
In this case, the first thing to review is very clear:is connected? Is the plug powerful? Look again power switch on the power supply, which is located behind the side of the cord as a general rule, since it is possible to accidentally compress it and the source is closed.
If you look at this and everything is fine, you may have accidentally hit the device and the power device connector has been removed. To confirm this you have to open the box and check in the motherboard connection area the «Power» cable is connected properly
Finally, you should check the other end of the cord, which is the one that goes to the index itself, even though this is complicated or small depending on the box. In any case, you can be sure the problem is on that thread or on the button itself To do the following: with the utmost care, with the computer connected to the Internet, insert a flat screwdriver (make sure it has a plastic handle and does not touch any metal) on the Power pins (PWR or PWR_SW) of the motherboard, and touch both at the same time with the screw.
With this you will open the phone as if you press the button. When it opens, you already know that the problem is the cable or the button. If it does not open, then you have a very serious problem and you should check the power supply with the mother board for the first time. In any case, it would be a good time to bring resources to that technical task.
When the computer opens but closes alone
Another symptom you may find is that the PC is light but only for a moment; the fans start turning and the lights flash, but then they go off on their own. There are situations where after doing this, it enters with an open and seemingly closed loop like it wants to try to start but can't.
In these cases the problem is It is usually related to processor or RAM. Start by removing all the RAM modules (with the PC power cable disconnected), leaving the computer out of RAM for a few seconds, then reinstalling it. If after doing that it doesn't start, try placing one module on one socket and installing it on another.
If after these tests the problem persists, the problem may lie in it motherboard or motherboard. The next step would be to disconnect the heatsink and processor, and then after checking that all the pins are OK, reassemble and try again.
If you did these two tests, it would be left to think that the power supply is not good, and the best thing you can do is change it to a new one.
The PC opens but shows nothing on the screen
If your case is that everything seems to work normally but nothing is seen on the screen, all you have to do is look at the cable connection first (be it VGA, DVI, HDMI, DisplayPort, etc.). Check that everything is well connected, that the light is on and you have the right source for the selected track in your OSD (if the view contains several inputs unchanged), and if possible try to turn the cable on.
If none of this works, try disconnecting the monitor cable from the graphics card (provided you have the drawings) and connecting it to the motherboard integrated video output (preferably HDMI). When the image returns, you will have to install the BIOS and select the default interface. If it doesn't give you an option, it might be destroyed your graphics card, so you have to remove it and restore it for the first time, checking that all connections are correct.