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Computer will not power on - Help needed

Posted on 2006-10-19
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Last Modified: 2010-04-26
I have a custom built system that has worked fine for about a year.  The other day the system will not power on.  When you press the power on button the leds flash for a second and all fans begin to turn but then nothing.  No changes had been made to the system hardware.  I pulled all the cards checking with each removal and still the same thing.  I also tried each of the two memory sticks individually and in different positions, same result again.  I pull and reseated the BIOS battery but have not chaecked it for voltage (need to bring a meter home from work).  The MB power light is on whenever power is applied.  I also disconneded the drives, DVD's, floppy, etc. with the same result.  I also pulled the CPU fan and reseated the CPU and fan again still the same problem.  I also disconnected the MB power caple and jumpered the Green to Black wires and the power supply started (again I do not have a meter to test the output).  Upon reconnecting the MB power cable I had the same problem.  All of this was last week and I did not have time to work on the system again until yesterday.  I turned the system on yesterday and it started?????  I restarted and started the system, powered off and retarted...  Everything was fine

Today I am back to where I was before and the system will not power up.  I started again as I did above and removed most of the cards.  When I disconnected the 4 pin CPU power cable on the MB and the power supply will start and the drives will run up when pressing the power switch.  Plug it back in and it will not start.

Any ideas as to where I should start?  Power supply, MB, CPU ????
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Question by:jllabs
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Christophermagee earned 125 total points
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Probably start with the power supply since that is the cheapest of the three, and a power supply is more likely to die than the cpu or motherboard.

Hope this helps.

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by:lukeca
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I would inspect your motherboard closely, look at the capacitators (the cylinder shaped things all over your board).  Check for any that are bulging on the top or are leaking.  If any of them have issues then your motherboard is the problem.
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by:imacgouf
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Hi,

An article from PCGuide with information on Power Supply, Function and Signal.
If your motherboard and components are being supplied poor-quality power, you will have problems that you wouldn't have if they received proper, high-quality power. If you plan on using your PC heavily, or if your data is important, or if you are looking for upgradeability in the future, you must pay attention to power! Power issues are responsible for more PC problems than probably any other single source, even though most people don't realize that the power is responsible. This chapter takes a look at power, both internal and external to the PC.
http://www.pcguide.com/ref/power/index.htm



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by:Freshcafe
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There shouldn't be a four pin CU power cable or connector even in a cutom built PC. Do you means the Hard Disk drive? Ther are standard Power connecttions for the Main Board and none of it directly connect to the CPU. (wake on LAN etc but not CPU). Two possibilties I can think of without seeing it or have all the info - PSU and HDD.

PSU not supplying correct power under load even if it reads correct voltage; when tested they usually are disconnected from the at least 1 system connection.

And the other is the HDD pulling down the system , drawing too much current.

In either case the above answer from imacgouf would be correct because either the 5Volt, 12Volt or power supplied is probably up to the standard.
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by:nobus
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i would replace the bios battery; if you can measure it, it should read 3 V
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by:jllabs
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Replace the power supply three days ago and no problems so far.  Thanks everyone for your help!
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