You switch on your computer and instead of the Welcome Screen the computer has given a series of beeps and the monitor is blank.  Why and what to do next?  If there are no beeps click here.

First some words of caution: Before opening up a computer case 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.  As a minimum wear anti-static wrist bands, suitably earthed, and preferably stand on an anti-static mat as well.  Remember to handle circuit boards carefully, touching only the edges.  It's a good idea to have a few old anti-static bags to hand where you can safely deposit components you take out of the computer.  Above all handle everything with care, it's very easy to get ham-fisted and cause real damage!  Finally, if you have any doubts about your ability take it to a repair shop.

Now back to the story...  When a PC is switched on the first thing it does, before you see anything on the screen, is go through a Power-On Self Test (POST).  If a problem is encountered during POST the computer gives a series of beeps.  In theory at least, the pattern of beeps indicates more or less where the problem lies.  Click here to see what the beep codes mean.  Use them as a guide and with luck they might speed up your search, but don't expect too much.  Broadly, if you have Award BIOS a single long beep followed by two short beeps indicates a video error, try re-seating the graphics card before trying anything else.  In particular make sure that the screw holding the card to the rear case slot isn't over tightened, especially if card and case are slightly misaligned.  This is a common problem and can pull the card slightly out of alignment with the motherboard slot causing a bad connection.  Also make sure that if the graphics card has a power socket the power feed comes directly from the PSU, and that no other components, especially case fans with poor quality connectors, are sharing the power cable.  Any other number of beeps and the problem is probably memory related, try re-installing the memory modules.  For AMI BIOS one, two or three beeps indicates a memory problem so try re-installing the memory modules before anything else.  Eight beeps suggests a video problem so try re-seating the graphics card and make sure that if the card has a power socket, that the power cable comes directly from the PSU and isn't shared by case fans or other components.  If you have Phoenix BIOS a single beep means that all is well and your computer is booting up as normal.  For anything else read on.

What to do

In the case of a POST failure - and this is what we're looking at - the practical options are fairly limited and it can save time in the long-run to spend a few minutes carrying out a few basic checks regardless of the specific beep codes.  The procedure depends on whether the computer is newly assembled or a few years old.

Newly assembled computer

In the case of a newly assembled computer the odds are that something somewhere isn't seated properly.  Open up the case.  Before you do anything else make sure any jumpers are correctly set.  If they aren't this could be the cause of the problem.  Assuming the jumpers are OK, carefully remove all the cards including the graphics card and remove the RAM modules.  Disconnect the power connector(s) from the motherboard.

Now make sure there are no stray screws or other debris rattling around the place.  Make sure the screws holding the motherboard in place are not too tight and that they all have fibre washers.  Give all sockets and contacts a quick shot with an air-duster to make sure of a good contact.

Now carefully reassemble everything, but leave out all auxiliary cards, only install the graphics card.  Make sure that everything is properly seated, paying particular attention to the RAM modules.

Replace the lid, reconnect and switch on.  With luck the computer should boot.  If it does you can put any auxiliary cards back in and if it fails top boot after you've done this you know where the problem lies.  If it doesn't boot, and all you get is a series of beeps again, switch off, disconnect and open up once more.

Remove the CPU and check for bent pins.  The reason for not doing this initially is that the CPU is probably the least likely cause of the problem and it's the messiest component to remove and reinstall.  While the CPU is out of its socket make sure no thermal compound has squelched onto the motherboard or CPU pins.  If it has, clean it off with thermal compound cleaner.  Always use thermal compound sparingly, only a very thin film is needed - a case of "less is more".  Silver based thermal compounds, because of their electrical conductivity, can be particularly damaging if they get onto the wrong places.  Also check for over tightness in any motherboard screws you missed first time round because they were obscured by the heatsink.  If you've separated the heatsink and CPU it might be necessary to clean off the old thermal compound and reapply.  With bent pins straightened, thermal compound cleaned up and screws checked and any problems sorted, carefully reinstall the CPU, close up the computer, reconnect and switch on.  If you still only get a series of beeps, switch off, disconnect, open up.  Reinstall the motherboard.  If this fails to do the trick make a strong cup of tea, take a deep breath and try to resist the temptation to hurl everything into the nearest skip.

It's now time to assemble a set of known working components and embark on a process of elimination by  remove a component at a time, starting with the RAM modules, and replacing with known working ones.  It's also a good idea to swap the keyboard - a long shot but you never know.  After each replacement try to boot the system.  If it isn't the RAM, graphics card or CPU its time to take out the motherboard and replace it.  As you've pretty well eliminated everything else, that should do it.