Help My Computer Won't Power On It's Dead

I don't know how many times I have a computer come in to where I work and it won't turn on. The customer says it was working yesterday and now it's dead. Well the first thing you can do is see if it will have any power at all. Do you see any leds on the front of the computer coming on at all. Generally you will have a power led of some sort and a led that flickers as the hard drive is running something. The other place to look is on the back of the computer. There are some power supplies that have a green led that lights up. Compaq and Hewlett Packard Computers may have this type. The led may be dim or flickering or not on at all. I would also check the power supply and see if it has a toggle switch on the back of the power supply. I have seen these for some reason get placed in the off position.
  The next step is to open the side panel or cover depending on the manufacturer. Most computers have one or two thumb screws that you will have to remove. You may need a Phillips Head Screwdriver to remove or loosen them. Now you can remove the cover. Try and power on the computer and check to see if any fans are spinning. If nothing is spinning then you can remove one component at a time to try and narrow down the problem. I have seen modem cards, usb cards, memory cards and other peripheral cards cause no power problems. I generally disconnect one component at a time such as a optical drive or hard drive to narrow things down.
  If the above steps did not help then it is time to inspect the motherboard and any boards for damage. The most common problem found are capacitors that are popped up on top and leaking or they can be blown out at the bottom causing the capacitor to tip. If you do find this then this indicates that the motherboard has taken a surge of power resulting in the overheating of the capacitors and thus damaging the motherboard. I have seen some technicians replace the damaged capacitors and once in a great while the motherboard works again. This only works if it were due to a time period when there were a bad batch of capacitors that went out. That happened a few years ago. My best advise is just replace the Motherboard , because usually there are more damaged components. You could have a situation where a component is damaged and may work for a short period of time or cause intermittent problems such as the famous blue screen of death.
  If the motherboard looks good and there isn't any damage, then I would test the power supply. There are good testers that you can purchase where you connect the various connectors to check the voltages such as the 12 volt line, 5 volt line and the 3.3 volt line. There are some testers that are fairly cheap in price. If you have a Digital Voltmeter you can be the true technician and test for these voltages. One of the best brands are the fluke digital voltmeters. If the voltages are bad I would test with a good known power supply if you have one. If you connect it and the computer powers on, posts tests and boots up properly just replace the power supply. If you have to purchase a new power supply I would recommend a supply putting out more than 500 watts. The higher the wattage the better due to have various drives and components in a system. Don't let someone have you put in a cheap 350 watt power supply. They were good a few years ago, but power consumption has changed in systems with new devices such a solid state hard drives and blue-ray players etc...
  Other problems I have found is a broken latch on a heatsink,  which causes the microprocessor to overheat resulting in the computer shutting off or not coming on due to it protecting the system. Another thing to check for is dust blocking fans, heatsinks and  air flow in general. You would not believe the amount of dust in some computers. They are so bad sometimes that bugs die inside the computer.
  The one thing I always stress is that before you touch anything inside the computer use good ESD protection. I have information in some of my earlier posts on this subject. You can buy a esd (electro static discharge) strap fairly cheap these days. If you need it quickly check out your local radio shack or electronics store. A quick way is to touch some bare metal to discharge any static electricity. I have heard some technicians say you can not damage a board when it is installed in the computer case. That is simply not true anything can be zapped and damaged.
  Thank You for reading and stay safe.