Not all motherboards give beep codes to signify POST failure.  Some just sit there and silently do nothing.  In these cases the procedure is pretty similar to the procedure when the computer does beep, except that there are a few preliminary checks to perform first.

What to do

First, check if the power supply is working.  Is the PSU fan blowing air out of the back of the computer, are any lights lit, does the DVD or CD drawer open and close then you press the appropriate button?  If there are any signs of life follow the procedures outlined on the previous pages <Link>.  If everything seems stone dead, don't despair.

First, if there's a power supply switch at the back of the computer make sure this is switched on (it's easy to forget this) and make sure that all mains plugs are fully pushed in.  'Lamp test' (by plugging an electric lamp into...) the wall socket or surge protector - whatever the computer's power cable plugs into - to make sure it's live and working, and for good measure try a different mains lead just in case the one you're using has a blown fuse or is otherwise faulty.

If you do this and the problem persists it's time to look inside the computer.

NB : Before opening up a computer case and delving inside switch everything off and make sure the computer is disconnected from the electrical source.  Before touching any of the components inside the case make sure you have the appropriate anti-static precautions in place.

With the case open make sure that the ATX power connector(s) leading from the power supply to the motherboard are properly seated and pushed home.  Above all make sure that the front panel power switch connector is correctly plugged into the motherboard front panel header pins.  This is especially easy to get wrong or overlook.

If none of the above work we're into long-shots.  You can test if the computer case front power switch is working by carefully shorting the motherboard front panel header power switch pins using a spare jumper, as shown in the picture.  If you're not absolutely confident about doing any this don't do it!  I've never had a power switch fail on a computer and don't know anyone who has, but you never know - it must happen sometimes.  If the computer starts when you do this, then the switch is the culprit and needs replacing.  If you can get at them they're usually pretty standard components.

Shorting the front panel header power switch pins

If still no luck, and to make absolutely sure you have a failed power supply and not a motherboard problem, disconnect the 20 pin Molex ATX power connector from the motherboard (this is at the end  of a bunch of cables leading from the power supply), and very carefully short the green wire to any of the black wires using a bit of bent wire or a paperclip.  Shorting pins 14 and 15 should do it.  The green wire (pin 14) is 'power-on' and the black wires, which include pin 15, are all 'ground'.  Now stand back and switch on the mains power to the power supply unit.  If the power supply fires up (fan spins) the PSU is probably OK and you have a faulty motherboard  (before discarding the motherboard try the procedures outlined on the previous pages, including re-installing it.  I've known dead motherboards spring into life when reinstalled<Link>).  If nothing happens when you power up, you have a dead power supply.

If the power supply is a cheap unbranded one this probably won't come as a surprising, but even high-end power supplies can die after a few years.

If the computer is dead but the power supply seems to be working, ie the PSU fan is spinning, there are lights lit etc follow the troubleshooting procedures outlined on the previous pages <Link>.