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PC won't boot up

Last response: in Components
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January 22, 2011 5:07:03 PM

Hi, I need some urgent help, 2 days ago I left my PC switched on and left to my office, I came back and found the PC switched off while the power was still plugged in and the power LED on the front panel of the case was still glowing but very dim. I tried everything..took the mobo out of the case and reseated it, plugged out and plugged in everything, even removed the processor and installed it again but nothing works. I had a spare athlon II so i changed the processor to see if there was something wrong with my already installed Phenom II but still the PC wont boot up. At Last i bought a new PSU but to my disappointment it didn't work either.

Now here is my observation, whenever I pull out the 4 pin sys fan plug it boots up but there is nothing on my screen, neither do i hear the beep sound at start up, just the cpu fan keeps spinning, the psu fan does not spin and the mobo on-board LED does not light up either. When I plug in the 4 pin to the sys fan mobo socket and press the power switch there is a slight movement in the cpu fan and the psu but it dies quickly after half a second. I have been trying to make this machine work but had no luck so far, its a new system that i recently upgraded, every component is new except the cpu case which is quite old.

Please help me, its getting frustrating :cry:  what is wrong here, is something wrong with my mobo due to some short circuit or is it the power switch on the case which is quite old. I'm so confused please help...... :??: 

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a b ) Power supply
January 22, 2011 7:21:52 PM

Very difficult, just reading your thread you would say psu or mobo.

Try resetting the bios.

There is a good troubleshooting No Post guide on here somewhere but I can't find it.

Can anyone else post a link or has it been removed?
January 22, 2011 9:15:35 PM

It cannot be the psu, I said I bought a new one today itself and still the same problem. About the motherboard I'm not sure and thats what I need help for. I say again when the 4 pin ATX cable that goes from the psu to the mainboard in the socket labeled as SYS FAN is plugged in, the system does not boot but for half a second then turns off, without the cable, system boots but just the cpu fan spins and nothing happens.
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a b ) Power supply
January 22, 2011 10:08:42 PM

The 4 pin P4 isn't plugged into the SYS FAN socket it is plugged into the 4 or 8 pin ATX socket on the board.
Without this plugged in properly the PC won't boot.
See below its the P4 or P8 depending on the slot on your mobo and what you psu comes with.

January 23, 2011 7:35:00 AM

Its a P4 connector for the mainboard ATX socket. To rule out any short circuiting due to cpu metal case I took out the mainboard from the case and assembled everything on a table, I tried to short the power sw pins on the board using a screwdriver.....the same f*** problem again, only the cpu fan powers up when the 4 pin atx connector is plugged out, when plugged in nothing happens just the fan spins for about a fraction of a second then it dies.
This rules out short circuiting and also that my case power switch is working fine. So it means its my mobo that is faulty. Its a msi mobo I bought 2 months ago....what went wrong I have no clue.
a b ) Power supply
January 23, 2011 9:04:44 AM

lucifer_9mm said:
It cannot be the psu, I said I bought a new one today itself and still the same problem. About the motherboard I'm not sure and thats what I need help for. I say again when the 4 pin ATX cable that goes from the psu to the mainboard in the socket labeled as SYS FAN is plugged in, the system does not boot but for half a second then turns off, without the cable, system boots but just the cpu fan spins and nothing happens.



You should not have anything but a fan wire connected to the socket labeled SYS FAN. This plug is for plugging in a fan. Not a power connector from the power supply.

Is this a 4pin fan header and you somehow connected a floppy power connector to it?
January 23, 2011 9:43:14 AM

From experiance, its your motherboard, and maybe your CPU as well, have you tried different motherboards, or the onboard graphics.

The motherboard will not boot without the 4 pin power socket pluged in, it will start for a few seconds then shut down.
As i say sounds like a MB issue

When you get this going again, set the machine to shut down at high temps in the bios, saves a lot of money and time.
MadBRiT
a b ) Power supply
January 23, 2011 12:03:51 PM

lucifer_9mm said:
Its a P4 connector for the mainboard ATX socket. To rule out any short circuiting due to cpu metal case I took out the mainboard from the case and assembled everything on a table, I tried to short the power sw pins on the board using a screwdriver.....the same f*** problem again, only the cpu fan powers up when the 4 pin atx connector is plugged out, when plugged in nothing happens just the fan spins for about a fraction of a second then it dies.
This rules out short circuiting and also that my case power switch is working fine. So it means its my mobo that is faulty. Its a msi mobo I bought 2 months ago....what went wrong I have no clue.


Have you reset the bios yet?

Has the board got a 4 pin or 8 pin ATX slot?
May 11, 2011 1:36:41 PM

You should try you're components on a different mobo , see if all of them work, if they do then so mobo is fried or something. check that the capacitors on you're mobo are not damaged( it happend to me once , one "exploded" - you should see a big "X" on top of a capacitor) or the microprocessors. also a cmos restart is good, leave the battery out for at least 1h.
May 11, 2011 2:02:08 PM

i know you stated it before, but double check if your ram is seat correctly.
Maybe try single strips or different banks.
Have seen it more then once, systems fail to boot up due to badly inserted ram.

Apart from that, seeing what has been done so far and you checked the cpu as well, the only thing remaining is the mobo.
Can you try your cpu in a friends rig as last test as well ?
!