Ok I have this problem for the last 2 years since I upgraded the bios for my P55WB.
My PC boot by itself for no reason!
I thought like some people told me that it's the PSU but I changed it last week with a brand new XFX,so it's not the PSU.
Some people told me that perhaps the PC's case power button is broken or something,I replaced the case as well with a new Thermaltake.
Another option was to disable wake on LAN but right now I don't have any network cable plugged nor wake on Lan ON.
So it's obviously the motherboard!
I upgraded to the latest bios but still no joy.
I even changed my graphic card but the problem was still here.
So how can I fix this damn problem??boot start
Please bear in mind that this product has reached its End of Interactive Support so Intel no longer provides interactive support for this product via telephone, chat or e-mail.
If you have replaced the power supply and chassis, you may try checking through power options in the system BIOS and set all settings in Stay off, for example set "After power failure" - Stay off
You might also test the system out of the chassis, placed on a non-conductive surface like a newspaper, a magazine or something similar, this to check if this related to a grounding issue.
You can also try a BIOS recovery as shown here:
Be sure to disconnect all peripherals not required for the update, even the mouse, keyboard, hard drives and any other CD/DVD ROM, this may take up to 15 minutes even if there is no display on the system
The file that you need to use is posted here: