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. romanian

    I had the same sudden shut down symptom at my C640 laptop. I tried the “cheap” solution indicated in this forum, namely to increase the mechanical pressure over the memory modules by adding some thin rubber over the modules. The computer, which I was going to throw away, works fine since then. Thank you!

  2. Laptop Freak

    Missy,
    Here’s the service manual for your laptop. It looks like you can access the fan if you remove the keyboard, it’s not very clear. If not, you’ll have to remove the top cover.
    This service manual has step-by-step disassembly instructions.

  3. Hello
    Can you help me out please
    I want to remove the dust from the heatsink of a Dell Latitude C640 but I don’t know where it is located.
    Do you have to remove the keyboard and everything or is there a little door just for the heatsink :)
    I know I gotta ground myself and remove the battery before to operate but that’s it :) lol
    I’ll try this because I have #M1004 Error Code.
    Thanks a lot for your answer
    :D MISSY XXX

  4. I’ve got a C640 1.7GHz/512RAM. I don’t know its history since I got it used for free, but the thing works great and I leave it on all day. It does like to run its fan a lot more than my Compaq Evo N620c does, but it never dies unexpectedly. The one weird thing it does is that the touchpad will randomly freeze up on occasion (everything else is still fine).

    And to the person who asked about the amber/green flashing light, that generally indicates a battery failure.

  5. I have a DELL C640 the same problems just keep shuts off
    but I’ve just found a simple experiment i use an external monitor and plug it to my C640 laptop and turn the laptop on the computer boots and runs great with the external monitor. This could be a good and quick check for the CPU, Fan and the memory but i am still working on WHY? the laptop works only when there is an external monitor plugged in to it and why not with it’s built LCD screen. Please if someone out there knows how to deal with this issue please POST

    Muruts

  6. Jonathan Evans

    I’ve read all the problems people have been having, and many of them look like the problem I’ve had with my Dell Latitude D600. Just like “Laptop Freak” and “Steve,” what I found was if I roll up some cotton gauze about the length of the memory stick and put it on top of the stick, then screw down the hatch, the pressure anchors the ram stick in place and prevents the weird random shutdowns. It was clearly a loose connection between the memory slot and the mobo: when it was working, if I simply tilted the laptop over onto one side or the other, it froze immediately. Now I can move it all around upside down, sideways, etc., and no freezeup. I imagine a good laptop or mobo repair technician could identify where the loose connection is–probably a solder joint has come apart–and resolder it solid again.

    Jonathan

  7. I bought a used Dell C640 not working condition with no hard drive When I turn it on (using the AC adapter)it goes on for seconds and then shuts off I notice the chassis fan doesn’t spin but then when would it since the unit doesn’t stay powered up long enough to make a judgement re the fan So where should I start?

  8. I took some photos of how i fixed my laptop. hope this will help anyone else who might run into this problem.

  9. Success!!!!!!! I cut up an eraser lengthwise and placed it on top of the RAM sticks and then screwed the cover back on. So far so good! No problems and lets hope it stays this way! Thank you for the all the help guys! You’re all the very best!!

  10. Laptop Freak

    Steve,
    Find a known good RAM module. Test the laptop with this module in both slots. First, install the module into the slot 1 and run it for a while, then do the same with the slot 2. Find out if the laptop freezes with your known good memory module, find out witch slot is bad. If the memory slot is bad, most likely you’ll have to replace the whole motherboard or use the laptop with one working slot.
    I have the same problem with one of my IBM ThinkPad notebooks. One of the slots is bad and the laptop cannot see RAM module installed into this slot. I was able to fix the problem by placing a small piece of pen eraser on the RAM module installed into the bad slot. When you close the RAM hatch, it presses on the eraser and the eraser applies pressure on the RAM module installed into the defective slot. It was enough to make a good connection between the memory and motherboard. It’s just a temporary fix but it worked for me.

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