computer wont turn on

[fishjie]

ok so heres the deal. my machine was functioning fine. i was trying to confirm that the fans were all working inside my machine, so i turned off the power and opened the case up. when i reconnected the power and hit the power switch the computer did not turn on.

i checked to make sure the jumpers for the power switch were connected properly, and they were.

i have no idea how to proceed from here. the green light on the mobo indicating there is power is on. yet when i hit the switch, nothing.

 

[LogitechFreak]

try plugging the power cord from the psu and flip the on off switch (if there is one) off and on then hit the power botton a few times then plug back in. if that doesnt work then try unplugging every power cable in the case then replug them back in one at a time. (make sure you have the psu's power cord unplugged when messing with internals)

 

[fishjie]

no luck. since the green light is turning on when i flip the on/off switch, can i rule out a problem with the power strip, the power cable, and the power supply?

 

[LogitechFreak]

hmm try reversing your reset switch and your power switch and try using the reset switch as the power button and see if it turns on then. if not you cpu might have bit the bullet.

 

[montag451]

What did you actually do inside your case when you opened it up?

Also, when you say that the computer didn't switch on - do you mean there was no power at all - does the psu fan spin?
Any mobo led?

 

[fishjie]

yes, the green LED on the mobo is on when i switch the PSU switch on (so again, this means that the PSU, power cable, and power strip are all fine right?)

however, when i switch the computer switch on, nothing happens (CPU fan and PSU fan and chassis fan do not spin).

now if this was a problem with the CPU being fried, wouldnt the mobo at least beep, and wouldnt the fans still spin?

when i opened up my computer i dont think i did anything wrong. i made sure i was ground and etc... although i did turn off my computer as it was booting up - can this potentially damage the CPU?

 

[montag451]

Just cos the mobo LED is on, just shows that some sort of power is getting to the LED.

Check the pwrsw on the mobo (powerswitch).
Try shorting the two pins on the mobo with a screwdriver to turn on.

If the cpu is fried, you might get a very brief spin or not, but most likely no beeps, depending on how shot it is.

Also, check that you didn't inadvertantly disconnect the 4 pin power lead to the cpu.

Try those two things and post back.
Oh yeah, no harm in resetting BIOS first - make sure computer is completely unplugged, then take out battery for a few seconds or so.

 

[fishjie]

i took out the cmos. i used a screw driver to connect the two pins (thanks i did not know this before, even if my computer is done for, at least i learned something out of it), but nothing happened. no beeps and no fans.

is there any way i can determine for sure the problem is with the CPU or with the motherboard? I guess the only way is to purchase a new compatible CPU, plug it in, and see if it works? I'm guessing plugging in an older CPU could damage both the CPU and mobo?

edit: actually one thing i'll do right now is rule out the PSU for sure. i'm gonna disconnect it and put it into another one of my computers and see if it works.

 

[montag451]

Nice one for checking psu.

Re- putting in an older cpu - is your cpu compatible with that mobo. If you are not sure, look in the mobo manual and it should tell you.

 

[chazzzer]

The LED on your motherboard is telling you that you have +5v from your power supply. Fans run off of +12v, as does your CPU (it's voltage is derived from the +12v rail). No fans and no POST is almost a sure indication that your power supply lost its +12v rail. When you hit the power switch the fans should spin, even without a CPU installed.

It doesn't mean for sure that your power supply is dead though...it could be shutting down the +12v rail because of a short circuit. Try unplugging the power from everything except the motherboard (hard drives, CD/DVD-ROM drive, case fans, et cetera). If that fixes it, then one of those things is shorting out your +12v rail. Reconnect them one at a time until you find the cause.

It's also possible that you crimped a stray +12v wire when you reassembled the case, and it's now shorting directly to the case (ground). Look where the side of the case joins the body of the case and make sure there are no wires crimped in there anywhere.

 

[fishjie]

thanks, that was an informative post. I was wondering whether or not the fans should spin even if the CPU was fried. However, I swapped out my current motherboard, with a known working one. I connected the power to my older one, and it worked. The fans spun. So I dont think its a problem with the PSU. I also ruled out the power switch, since when I connected the POWERSW jumper to my working older mobo, the on button worked.

to test your short theory, I did as you said and also disconnected everything except my mobo to the power supply, but it still did not turn on. The on button didnt work, and even shorting the POWERSW with a screw driver did nothing. I made extra sure that there were no wires that could cause a short.

Is it possible the problem is in my mobo? Somehow the green led is still turning on, but for whatever reason, the fans wont spin and it wont POST?

Well I've decided to just purchase a new CPU and mobo combo anyway.

If anyone else has ideas until the parts arrive, I'll be glad to try them. If anything, this thread has been very informative to me, and I've learned some useful info.

 

[montag451]

Hi,
When you disconnected everything, did you keep your cpu/fan plugged in.

If the cpu isn't connected, NOTHING will happen when you switch on.

 

[fishjie]

yeah cpu/cpu fan was still plugged in

but chazzzer said the fans should still spin even if the cpu isnt in. so which one is it?

btw i had an idea about the 12 v. i have a voltmeter, so how would i use it to check that the psu is outputting 12 v?