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Computer starts and turns off after 2 seconds. Then cycles

Last response: in Systems
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August 21, 2011 3:00:06 AM

My system has been in storage for 3 months. I hooked it hotbox week an when I turned it on it shut down after 2 seconds. No post. After 5-6 seconds it tried to power up again but failed. It will cycle like this until I disconnect power. The case fans and ps fans turn on when I turn the computer on. The cpu fan and vc fan don't but they twitch when it powers off. I reseated the heatsink ad checked all the connections. I powered up with disconnecting the 12v atx to the mobo. It started but with no CPU running obviously. Any suggestions?
August 21, 2011 3:01:50 AM

Gigabyte ga-ep45-ud3r
I think e7300
Corsair 450
Sapphire 4850
4 gig g skill ddr2 800
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August 21, 2011 3:11:21 AM

well since you checkd all the connections already , try resetting the mobo cmos battery by removing it and reseating after a few minutes. a similar situation happened to me on a pc i was repairing and my suggestion worked for me.

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RSL1989 build:
-MSI P67A-G45 (B3) LGA 1155 Intel P67 SATA 6Gb/s USB 3.0 ATX Intel Motherboard
-Intel Core i5-2500K Sandy Bridge 3.3GHz @4.0 OC Quad-Core Processor
-ASUS ENGTX550 TI DC TOP/DI/1GD5 GeForce GTX 550 Ti (Fermi) 1GB 192-bit GDDR5
-Seagate Barracuda ST31000524AS 1TB 7200 RPM SATA 6.0Gb/s / -LITE-ON DVD Burner 24X
-G.SKILL Ripjaws Series 8GB (2 x 4GB) DDR3 SDRAM DDR3 1600 (PC3 12800)
-Rosewill RV2-700 700W ATX12V SLI ready / -Rosewill FUTURE Gaming ATX Mid Case
-Sunbeam RHK-BA Rheobus 4 Channel 20W Fan Controller Panel / -6 Rosewill 120mm Blue LED Fans
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August 21, 2011 3:16:58 AM

I did reset CMOS and it still hasn't worked. From what I've read it sounds like the shutting down is a safety issue for overheating CPU but I hardly think it would overheat in 2 seconds. I thought maybe the ps was bad but the fan still runs and I tested some ofthe other connections and they worked. I'm thinking maybe the mobo or CPU is bad...
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a b B Homebuilt system
August 21, 2011 3:49:44 AM

Some mobos will shut the system down immediately if they start the power up cycle and do not detect that the cooler fan is spinning. So that's one place to look. They sense the rpm via wire 3 of the 3- or 4- pin connector from the fan to the mobo. Check if the fan is spinning and perhaps r/r the connector cleaning the mobo pins.
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August 22, 2011 5:45:22 PM

I've tried everything I can think of and all suggestions on got on here. It still won't work....
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a b B Homebuilt system
August 23, 2011 6:39:48 AM

I had a Dell system with similar symptoms once . . . if I manually spun the cpu cooler fan almost immediately after pressing the case power switch the system would start up and the cpu fan would continue spinning on its own.

You could also try connecting one of your case fans (if its 3-pin) to the cpu fan socket. If a bad fan is preventing BIOS from starting up, this would fool it into thinking all was ok. Obviously, it won't cool your cpu though :) 

If I had a spare psu, I'd swap it in and see if that's the problem. If its not the cooler fan or psu, the next candidate in line would seem to be the mobo.
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November 23, 2013 8:44:10 PM

How to solve a "power cycling on and off" problem.

When confronting a "power cycling on and off" problem, If you know how that system works, it makes it easier to trouble-shoot. Never do work inside the computer if there is power connected to the power supply. The computer is alive unless you turn the power supply switch off or unplug the main power cord. The main board uses the 5 volt line to keep the computer ready to receive the on or off command. The main board turns the computer on by grounding out the green wire going to the 20/24 socket ATX power connection. If you turn the computer off, or the main board detects a catastrophically unsafe condition, the main board disconnects the ground from the green wire.

There are several things that can cause this "power cycling on and off" problem.
The jest of it all is, the main board is reacting to an error, or an unsafe condition. The three most common problems are; the main board sees No CPU fan, the main board thinks the CPU is at an overheated condition, or the main board is bad. If the CPU fan is bad, not plugged-in, or you are using a fan with only two wires, this meets the "no CPU fan" error condition. For the CPU fan connection, a fourth wire is not necessary, but a third wire is. A bad CPU, the CPU's 4/8 pin power connection is not plugged in, a poorly installed cooler, or a bad CPU temperature sensor, can all cause an "overheated CPU condition" error.

If the voltages that are coming from the power supply are incorrect, or being dragged down by a short, this can also cause this error; this is unlikely, but worth checking. The Graphics card, BIOS and memory are three other possible but unlikely suspects. At this stage, the quickest way to troubleshoot this problem is to first check and reseat the main board's two power connections and CPU fan connection. Now check to see if you still have the problem. If you do, reset the BIOS, and try it again. If you still have the problem, Let’s do a minimum systems check. Remove all memory, unnecessary connections, and cards from the main board. Leave the case connector ("on and reset" button, LEDs, 4 pin speaker) and CPU fan connection only. Plug the two main board power connections (ATX and CPU) in from a "known good" power supply. Now check to see if you still have the "power cycling on and off" problem. If the problem went away, one of the items you unplugged is bad. Check them by adding them one at a time. If you still have the problem during the minimum systems check, there is one last area to check; the CPU. I have also seen a poor connection between the CPU and its socket, cause this problem. If that connection is good, if you have an extra "known good" CPU you can install, do so and check to see if the problem persists. If that also failed to solve the problem, there is little to no doubt that you have a bad main board.

NOTE about checking the power supply: If you wish to check the power supply by its self (stand-alone), bend a paper clip into a U-shape. On the ATX connector, plug one end of the paper clip into the green wire's socket, and the other end into any black wire's socket (ground). To turn the power supply off, just remove the clip. In effect, you are turning the power supply on and off the same way the main board does. As the power supply turns on,its fan will start running. You can now check all of the voltages with a multi-meter (under "no-load" conditions). Every Black wire comes from the same place, GROUND. When working inside the case, always remove power, and then wait for the main board's power light to go off. If it doesn’t have a power light, wait 10 seconds before you proceed.

Not every main board acts or reacts the same way, There are no perfect universal trouble shooting guides.
However, this is a good general well-balanced guide, and will work well on any ATX main board.
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