MB turns on by itself

[ninetears]

Hello everyone. I have a bit of an unusual problem here. I have an old PC with MSI K9N Neo V3 motherboard and when I turn on the switch on my PSU the all fans and components turn on by themselves even though I didn't press On button on PC case. The system does not boot up, only when I press the On button it starts and then everything works normal. When I turn off computer using Shut Down option in Windows, monitor and HDD shuts down [I hear that little click when HDD powers off] but the fans continue to spin and I have to switch off PSU button to turn it off completely.

Now, I've checked everything from RAM to the front panel connectors. In the end I tried turning the PSU on with nothing but the PSU and CPU on motherboard [I removed even the front panel connectors] and still the fan of CPU and PSU automatically spin. I even replaced PSU and I still have the same problem.

I also checked the BIOS options, and everything seems to be fine. Last night I used PC analyzer and I get the code 40 00 [when the system is up] and then 04 40 [when the computer is shut down via windows and fans continue to spin]. I have no idea what those codes mean, and that little book is of little help.

Does anyone have any idea what the problem might be? I figured out it must be bad MB, since it's pretty old and I have no idea what the previous owner did to it. Thanks for help.

 

[BadActor]

It might not be a problem. Some older motherboards had a feature that allowed the board to be powered for USB charging or music playback via the CD drive, even when the system was powered off. Not sure if this is the case with your board, but you could test to see if a USB device charges when powered off. You might try changing the sleep states or disabling and see if this has an effect. You might also try loading the optimized and fail safe Bios configurations.

 

[BadActor]

http://www.tomshardware.com/answers/id-2180070/usb-charging-computer.html