OptiPlex 755 mysteriously turns itself on

[Ascetic]

My optiplex 755 turn off but randomly turns itself on after few seconds. I have purchased this computer last month and having a mysterious issue on power. I got it with 32 bit vista and i reinstall 64bit version. The detailed description of my problem is when i turn off my system after few sec it will automatically starts itself but never boots to windows. The fan sound is too loud. Along with the power button, only the numbers "3" and "4" are lit green. When i remove the power cable and again connect the power cable and start the PC the system will boot to windows fine. Does any one have any solution to this problem?

[Devasis]

Even i have the same issue with my Dell computer but it get resolve as time passed. I could not figure out the underlying cause. when you boot your system press F12 and enter the BIOS settimg. In BIOS setting see that wake on lan is off. If it is already off the the issue is with the motherbord. Contact Dell support for more knowledge to fix your problem.

[MrChris-]

What bios rev do you have? Try to perform this it might help you. Reset the memory and Go to Advanced system properties and select "Startup and recovery" disable the Automatic Restart. System failure seems to have resolved this issue. this may be due to overheated, a wrong setting in the DOS. i am not sure whether you will be able to get it working again if you are not an expert.

[Lillebror]

I think it is happening due to one of the following reason.
1) It would likely be due to overheat. The heatsink on your processor is not on tight enough and computer shuts down to keep it safe from dying. If you are moving your system around then this is the most likely to happen.
2) A dud power supply. it sometime happen because of PS that fails to power the CPU.
There may be some other advance problem but this are the most likely.

[jesse]

Buddy, Does the motherboard replacement fix the issue? Because I have 755s that is also having such type of problems of auto restart when I shutdown it. And it will boot only unplugged for few minutes. I have given call to Dell tech support they told to update the BIOS. I downloaded the updated version but this trick even does not work either. Should i also replace my motherboard?

[Humberto]

I did not actually replaced the motherboard but now this problem has gone away. I am not sure what fix the issue but I had made two changes to the system. I was running vista 64 Bussiness edition and I had plugged an APC battery backup via USB. I just unplug the battery and uninstall the vista 64 and install the fresh copy of vista 32 bit version. Now the problem is get resolve. I have not yet try plug in again my battery and see whether the problem reappears again. I will try it in future and will post the result.