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Computer Won't Turn On? Beep Codes, Lights, and Fans

written by: Jesma•edited by: J. F. Amprimoz•updated: 6/3/2009

In part three of this series on troubleshooting Why Your Computer Won't Turn On, we discuss flashing lights, beep error codes, and partial power issues.

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    The Lights On The Front Of Your Computer Turn On or Flash, But Nothing Else Happens.

    Usually this is indicative of a failed power supply. In my experience, 80% of the time that was the case, 19% of the time it was a failed motherboard, and 1 time (not 1%, just 1) it was a rare error involving the front panel controller board. Most computers don't have extensive controller boards in the front panel but Dell seems to favor them heavily. To troubleshoot a failed Power Supply or Motherboard please refer to the previous installments of this series.

    Your Computer Emits Loud Beeps or Tones

    These noises you are hearing are called Post Error Codes or Post Error Beep Codes. Different combinations of long and short tones indicate different potential problems. Most computers will emit one short beep when they "pass post". Post stands for Power On Self Test, and is a series of checks your computer does on itself to make sure it is working properly. A single, short beep is the "All Clear" message.

    The interpretation of the Beep Code you hear is entirely dependant upon your computers BIOS or manufacturer. If you do not know what BIOS type your computer is using, call your computer's manufacturer and ask. If they can't tell you, then you will probably have to do an internet search of your motherboard's model number, which is usually painted on your motherboard.

    The interpretations for all the different motherboards is far too long of a list for me to disclose here, but this website has a very good and complete list.

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    The Computer Lights Up and Fans Turn On, But Nothing Else Happens

    This isn't a very common problem as most of the time computer components are either working fine or not working at all. Occasionally, though, a Power Supply that isn't regulating voltage correctly or has stopped producing the right level of power can cause an error like this. This can be a difficult problem to identify though, since there's very little indication that your computer is or isn't completely "booting up". Most, but not all, computers give an "all clear" POST beep when you first turn them on. If yours normally does but in this case does not, then you are more than likely looking at a faulty power supply. If your computer doesn't normally beep once as it is booting up then hopefully you know your computer well enough to identify the clicks and whirs it produces when it is successful. Part one of this series deals with troubleshooting power supplies and other electrical factors.

Computer Troubleshooting - If Your Computer Will Not Turn On

"HELP! My computer won't turn on!" As the owner of a PC repair shop, these are words I hear every day. Find out what the most common causes are and simple steps you can take before bringing it in for repair.
  1. Computer Won't Turn On? Electrical & Power Supply - Problems & Solutions
  2. Computer Won't Turn On? Troubleshooting the Motherboard
  3. Computer Won't Turn On? Beep Codes, Lights, and Fans
  4. Computer Won't Turn On? Video & Display Problems
  5. Computer Won't Turn On? Troubleshooting Memory (RAM) Problems