Dell Latitude C640 shuts off all the time

Hi, I have a Dell Latitude C640. It shuts off all the time and can usually only get windows loaded and it’ll shut right off, then it will turn on and turn off right away at boot. I’m very familiar with taking these apart and when this first occurred I suspected a clogged cooling system. So I checked, and it was clean as a whistle… hmmmm…so I’ve been looking for anything out of the ordinary on the motherboard but everything is tight and looks clean. Even took the LCD apart to make sure there weren’t any loose connections. So if you could give me any insight on this it would be a great help! The only thing that “SOUNDS” suspicious to me, is that sometimes I can HEAR the power when I plug it in, a very faint high pitch ringing noise…. so then I figured well if its the plug technically it should still run fine off the battery, but it does the exact same thing. I’m also suspecting that maybe my fans aren’t running fast enough?? Or maybe I need some new thermal grease on the CPU??? HELP!!

Yeah, looks like an overheating problem. By the way, have you checked if the fan spins at all? May be it stuck and causing this high pitch noise?
I would probably remove the hard drive and boot the laptop from a Knoppix CD. Knoppix is a live Linux CD and it will boot your laptop to a Windows like environment. You don’t need the hard drive to boot the laptop with Knoppix, only the DVD/CD drive. If the laptop boots fine and doesn’t shutdown, then something is wrong with the hard drive or with the operating system on it.
Also I would test the memory module. You can run Memtest 86+ and see if the memory fails the test. It’s possible, that the memory works fine for a while when it’s cold, as soon as it warm up it fails. That’s why your laptop works fine for some time, and then just shuts down when you restart it. If the laptop doesn’t run long enough to finish up the memory test, then try to replace the memory if you can find any test module.
Of course, I would try to reseat all connectors inside the laptop. Any loose connection might cause this problem.

167 Responses

  1. FIXED IT!!!!… YES…YES….YES!!!!!! …..and within 5minutes!
    It started like this: My Latitude C640 was working fine. I seldom used it except on vacations and it was kept in its case. However, I took it out and updated everything since it hadn’t been on for about 6 months when I was in Florida. I turned it on two days later and it wouldn’t boot. Sometimes for maybe 2-3 seconds up to a minute, maximum.
    I tried about everything and was ready to kiss it goodbye until I read a posting. The solution just seemed to simple but lo behold, it worked. To boot it, I pressed and held down the power button for 20 seconds and it booted for about a minute. I tried it again and continually held it until it completely booted up.
    It is working great now.

  2. so when the fan isnt moving, that means it’s an overheating problem? because when i blow in it , it goes, then stops….

  3. Hi
    Other things can cause a laptop to turn on and off. Like the ram is going bad in it. I had one of those a few weeks ago. Tested the computer with pc check v6 disk and the ram failed.

    My question is that I am not sure on…Is if you have a latitude c640 and it isnt upgradeable to run windows 7 but you are running it witn only 768 mb ram and 100 gb hd. with its original motherboard and cpu…Would it slowly fry the motherboard because its running something that needs more ram then what the system can provide?

  4. frankie


    i scored a dell c810 quitte cheap ..
    he turns on and off after a few seconds..
    i opened the lap and i saw there a small powerboard at the front onder the touchpad
    might the small board be the problem or is it a fet to the cpu-power?


  5. Flusensieb


    @112 Emiliano: Thank you for this information.

    I fixed a C640 in the same way Emiliano did.
    I replaced the damaged IC on position U45 on the board with a very small selfmade circuit board.
    I put a BC 807-16 SMD (similar to 2N2907) transistor with a 15K Ohm (SMD) resistor in the base on this selfmade circuit board.
    I used some wires to connect U45 and this small board.
    No it works great.
    Thanks for your help!

  6. frankie68

    hi ali,

    i had the same with a c640 board..
    as soon as i plugged the adapter the adapter goes off.
    so i soldered some things from another c640 mother board as a experiment and put it on the c640 ..
    at least he turned on ! but the short came back after two minutes..
    i replaced the 8-leg ic right behind the jack (on top)
    and one of the 8 8-leg ic’s on the very right side (close to
    the video connection)
    so the short should be somewhere there (i think)

  7. ali alazzawi

    in the first my languge is not very good
    so i will try to explane my problem as i can
    i have laptop dell latitude c600 and when i plugg the AC adaptar it will turn off and i will plugg the ac adaptar in another laptop it will work fine
    then i know the problem in my moatherboard so iwant to learn how i fine the short in my board

Leave a Reply