Computer wont post

By Niksko
Apr 2, 2006
  1. Ok, my computer wont post. Today, I took out the old mobo and installed a new one. Then i proceeded to re-connect all the leads and cables. Then when I tried to turn on the computer after hooking it up to the power supply, it wouldn't even startup. I thought I might have gotten the power button cables the wrong way round, but then i realised that there is no right way round and they work either way. After a little bit of tinkering, I got the thig to turn on,but it turned off again after about 1 second. I played around a bit more and eventually realised that if i cleared the cmos, and then returned the jumper to the default position, it would turn on and then go off again, like before, and then on subsequent presses of the power button, would do nothing. Basically, if i reset the cmos,it will turn on and then go off 1 second later. Any ideas on how to solve the problem? The mobo is a k7s5a and i have a geforce mx400 graphics card. sorry, but i dont really know much more than that because the mobo was given to me by a friend and it allready came with the processor and ram.
    Help would be greatly appreciated because my parents will kill me if i dont fix this for them.


  2. DonNagual

    DonNagual TechSpot Ambassador Posts: 2,404

    Well, first two things that pop into mind are:

    1. Did you clean off the thermal pad and put some new stuff on there before you put the heatsink on, or are you trying to use the old thermal pad?

    2. Did you use the riser pins to separate your motherboard from the case?

    Have to ask ;)
  3. kirock

    kirock TS Rookie Posts: 1,221

    Sounds like the CPU is shutting down from overheating. Check that you installed it correctly and the heatsink/fan is installed correctly. You must use thermal paste/grease on the top of the CPU, the interface between the heatsink and CPU surface. Some have a thermal pad installed there, make sure it's there don't remove it unless you use thermal paste. Is the CPU EDIT:FAN(missed this word) plugged into the mobo, is it turning when powerred up?
  4. Niksko

    Niksko TS Rookie Topic Starter

    DonNagual - When i got the mobo off my friend, the cpu was allready installed, as was the heatsink and fan. Yes i did use the riser pins (although they are metal.could this be shorting the mobo?) and i can't see the mobo toutching any of the case walls.

    Kirock - Yeah, i thought it might be that too because the heatsink is so big that the psu actually cuts off half of the fan,but i unscrewed the psu and left it half out of the case and then hooked it up (ie. the psu was no longer blocking the fan) and it still gave me the same problems.

    Also, if it does turn out to be the psu blocking the fan (which i know is a very bad thing), what can i do about fitting the psu in the case so it wont cut off the fan?

  5. kirock

    kirock TS Rookie Posts: 1,221

    Is the a micro ATX case then? I've never heard of a PSU blocking the CPU fan before in a standard ATX case and ATX PSU. Interesting.
  6. Niksko

    Niksko TS Rookie Topic Starter

    Not sure if it is a micro atx case. Could it be that the bios battery has run out? If so,would you suggest getting the battery from the old mobo and switching it with the one in the new mobo? could the processor be blown? How could i check this?


    UPDATE: I'm about to go to sleep, but i thought i'd give it one more go. I plugged the power cord into the computer, and it turned on ( I forgot to mention that it turns on by its self as soon as i plug it in to the power) but it still just turned off again. This would seem to indicate that whether it turns on or not has nothing to do with the CMOS reset, but simply to do with whether it is a warm or a cold restart. Does this help?
  7. Niksko

    Niksko TS Rookie Topic Starter

    Ok,this morning, i plugged it into the power, and it did the usual thing of turning on then turning off. When i went to unplug the cord from the psu, i must have jiggled it a bit, because the computer sprang back to life, and i finally got it to post. Figuring that the problem had been solved some how, i turned off the computer as i had nothing else plugged into it. Then i tried to turn it on again, but it had gone back to the old thing. Damn!!! But this would seem to indicate a problem with the psu. Comments?

  8. kirock

    kirock TS Rookie Posts: 1,221

    Well it it is hard to say, but from your first description of the prob, DonN and I both simulataneously (and independantly I might add) hit upon the same conclusion, CPU overheating. With that being said your new details might include the PSU as part of the problem, or it could also be the prime culprit. PSU are not very expensive (well compared to the purchase of the PC itself), can you buy or borrow a replacement to rule out this factor?

    Cheers and keep us posted.
  9. Niksko

    Niksko TS Rookie Topic Starter

    Ok, a few things.

    1. I have tried switching the psu with another one that i had, and it still wouldn't work.

    2. I figured that it might be better to just switch back to the old mobo and once i get that working i can set about getting the new mobo to work. I've just finished installing the old mobo back in, and now it wont work either. This is really bad. But this would seem to mean that it may be a problem with the way i'm installing things since it now will not work with it's original PSU-mobo combo as well as other combinations of the two. What sort of mistake could be causing this? I have triple checked all conections are properly put in and connected to the right things,but some pointers as to what sort of wrong connections could be causeing this would help.


  10. Niksko

    Niksko TS Rookie Topic Starter

    Ok, after reading around, I thought it might be a good idea to assemble to computer outside the case. In case you dont know what i mean, i got the motherboard and placed it in it's box. Then I put in the VGA card and hooked up the mobo to the psu (also out of the case). Then i plugged the psu into the power and used a screwdriver to effectively short two pins on the mobo that are supposed to connect to the power button. To my surprise, the thing booted up and i got some text on the screen. From the reading ive done, this would seem to indicate that all the parts are working properly (since it wouldn't boot with the same configuration in the case) but the case is touching the mobo and it is shorting it. If i'm right in saying the mobo is being shorted, how can i go about stopping this?

    Quick replies would be appreciated because my parents are about to kill me


  11. kirock

    kirock TS Rookie Posts: 1,221

    There are insulting washers which are to be used bwtn the mounting screws and the mobo and/or the stand-offs and mobo (if standoffs are metal). Usually these are just thick paper disc. Look around for these in the mobo box.

    gotta run to work, check bk later.
  12. Niksko

    Niksko TS Rookie Topic Starter

    Unfortunately, when i said that the mobo had been given to me by a friend, i meant that he no longer needed it. Thus, it had allready been opened and there are no paper washers to speak of. Is there any way i could buy or make them ie. could i simply use small cardboard squares?

  13. kirock

    kirock TS Rookie Posts: 1,221

    Absolutely cardboard squares will work just fine. I recommend one on both sides of the mobo at each screw and stand-off point, just to be doubley sure.

    I always point out the mobo shorting thing/stand-offs/insulating washer. But then the last couple of times, I got flamed sort of, "I know how to build a PC, this is my blah blah number of time...." rant, so I thought I wouldn't mention it this time. This one's for me: :unch:

    Hopefully you found the problem. Let us know. :wave:

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