Computer wount stay on for more than 3 seconds

[r3ddyfire]

Asus m2n-mx se plus mobo
amd athlon x2 2800+
1gb ram corsair
not sure about power supply it says on it: "high quality p4 power supply" a weird looking symbol and a 480 after it. its max output is also 480.

i decided to be a smart ass today and i pulled a tv tuner card out of the pc while it was on. immediately the system turned off and when i went ot power it back on it cranks over for 3 sec then goes dead no beeps lights or anything.

before you say anything i have been reading ever thread in here remotely related to my issue and i have tried all the different suggestions.

cleared the bios cache thing (moved jumper, pulled batt)
set up the mobo on a cardboard box and powered on by shorting the power pins
ensured cpu fan is plugged in and operational, replaced with other fan
switched psu
cant really try another cpu since i dont have a spare one and same with mobo.

the weird thing is if i pull the 12v cord off the mobo it'll power on and stay on however it will not boot or beep or catch on fire or anything.im getting a multimeter tomorrow so i can do some better diagnosing but i am not quite sure how to use it yet.

so if anybody can come up with a suggestion of any sort by all means let me know

here are some pics...might be usefull for whatever reason

http://www.youtube.com/watch?v=rO08Tkeg-BA

 

[jsc]

First thing, get a better PSU. The label says "maximum power". I'd bet it couldn't feed 300 watts into a modern computer. A 16 amp 12 volt rail is pitiful.

Get one of these:
Corsair 400CX (30 amp 12 volt rail)
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139008

 

[MMclachlan]

I wouldn't be surprised if you've killed it. The motherboard at least.
I once plugged an ISA gameport card into an IBM AT when it was on and that did a similar thing - mine made a nice pop.
You might be able to save the ram/cpu - try testing them in another machine if you can.
You've learnt something though - standard expansion cards are not hot-swappable!

 

[jsc]

Oh, crap. MM, I missed that. I was focused on one tree and got lost in the forest.

OK. Troubleshooting time:
First, leave the system out of the case. Assuming that you have a way to turn your system on, what you have there is a breadboarded system - a system built without a case on an insulated surface.

Work through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-posting-boot-problems
I mean work through, not just read over it.

Breadboard - that will isolate any kind of case problem.
http://www.tomshardware.com/forum/262730-31-breadboarding

The breadboarding thread has a paragraph about how to build and test a PC in stages.

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU. It looks like you do not have a case speaker installed, right? If not, you really, really need one. If your case or motherboard didn't come with a system speaker, you can buy one here:
http://www.cwc-group.com/casp.html

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.

At this point, you can sort of check the PSU. Try to borrow a known good PSU. 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. The 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=youtube_gdata

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 you get the long beeps, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card. Silence or long single beeps indicate a problem with the memory.

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.

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.

 

[r3ddyfire]

I don't know if you guys noticed or not.but.I have a.YouTube video of me turning the system on outside of a case. I can get a good pay and a speaker to attempt the trials you mentioned. Thing is psu starts and runs just fine. Again the pc stays on if I don't connect the 12v cable. Which I think is completely weird. Thanks everyone for the quick answer.

 

[daship]

You need a motherboard speaker.

And your ram is in the wrong slot. Or you got a backwards motherboard.

 

[MMclachlan]

Quick diagnosis from what you've said is dead motherboard. You have likely damaged some of the components on the board with your houdini card removal trick, either created a surge or a short, and it has stopped. The power supply will still spin up as what you've done is likely to be affecting a lower voltage circuit on the board, not big enough numbers to kill the PSU.
What I suggest you do is try the initial steps as jsc has outlined, try testing with a speaker and see if you get any error beep codes etc (which I personally doubt you'll get). Once you've done this and if you get nothing I'd say you can resign yourself to the fact that the board is toast. (RAM slot doesn't matter, it should boot in either slot) The only thing left to do then is test the cpu and ram in another working machine if you have access to one and then either buy another motherboard or start again. To be honest its all pretty old stuff so if initial testing reveals nothing I'd just look for another barebones bundle, you should be able to pick up a cheap dual core and 2gigs of RAM bundle for pennies on Ebay.

 

[r3ddyfire]

ok well im leaning towards the motherboard being dead as well the thing that is bothering me is that the little green led is on once i turn the psu on. also i put a case speaker with it and got no codes whatsoever.
i used another psu i found around the house that was a bit more powerfull (see image below)

last question i have is. what does it mean if the board stays on if i dont plug in the cpu cord from the psu? wouldnt that mean i fried my cpu rather than the board itself ?let me know if you want a video of this process ...