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Wont boot just flicks on and off straight away

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December 28, 2010 1:12:17 AM

Hello,
my computer wont boot
it just flicks on and off striaght after i press the power button... i have taking out any unnececary components and replaced the power supply..does this mean the cpu or motherboaard are fried???
December 28, 2010 2:27:09 AM

ive had the same problem before, with the screen quickly disappearing. does the cpu fan/ psu fan run after the screen flickers? any beep noises being made? have you tried different monitors? any info you can provide would be more helpful to us.
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December 28, 2010 2:56:57 AM

nothing was running afterwards..and i didnt have a computer speaker...i started from the start installing the components untill i found that the HDD was the problem ..mustve kept shorting it out or something.
thanks
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December 28, 2010 4:53:06 AM

argh now the keyboard and mouse dont work(well they do in the bios)but not when i finailly get to the install of windows 7...im thinking the motherboards fried
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December 28, 2010 5:20:27 AM

damn... im sorry. if there both plugged in at the ps2 port, try to use usb keyboard/ mice. not really a fix, just a temporary patch. and if they work in the bios, i cant comprehend why they wont work in the install. you could always try a different version to test, i.e. linux, or xp, pending on your tastes.
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December 28, 2010 8:42:04 AM

thanks i will try a different OS..i have tryd different keyboards both usb and ps2 also a usb keyboard with a ps2 adapter....
it seems to be failling everything when it comes to install and u need to select the keyboard layout ect,like the mouse and keyboard lights switch off
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December 28, 2010 3:34:23 PM

Work systematically through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

If not, continue.

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

Breadboard - that will help isolate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboardi...

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

Make sure you plug the CPU power cable in. The system will not boot without it.

I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case once you are finished.

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card.

Silence, long single beeps, or series of short beeps indicate a problem with the memory. If you get short beeps verify that the memory is in the appropriate motherboard slots.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.
At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
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December 29, 2010 6:15:01 AM

thank you tryed alot of these think i need a new mobo
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January 10, 2011 5:35:04 AM

it eneded up being one of my ram sticks and the HDD shorting it out,systems back up and running
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October 19, 2011 6:10:17 PM

kez182 said:
nothing was running afterwards..and i didnt have a computer speaker...i started from the start installing the components untill i found that the HDD was the problem ..mustve kept shorting it out or something.
thanks


hey can you help me i'm having the same problem i hit the power button and the blue led on my pc clicks on and off. and no sound at all comes from it, like the sound of the fans spinning inside the harddrive, and no visible fans spin either
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October 19, 2011 6:31:23 PM

Reseat cpu
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October 19, 2011 6:36:27 PM

how do i do that? what do you mean take my processor off and put it back on?
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!