This was a request from a few people who I've seen on the forums having problems with their ASUS p8p67 PRO B3 doing weird double or triple boots. I too had this problem and was able to stop it from occurring.

I will go through the steps I took to eliminate the problem. Please know this isn't a definitive guide or all the answers to the problem, but these things did work for me.

Background information:
The system build I have is:

- i7 2600k @ 4.3GHz
- G.Skill Ripjaws XL 8GB DDR3
- GTX 570 OC
- Vertex 2 60GB SSD
- P8P67 PRO Motherboard B3

My system was OC'd to 4.4GHz using the "XMP" setting – this also put my RAM at 1600MHz. At some point I accidently changed this (causing further issues which I'll explain later).

First things first – clear RTC RAM:
NOTE: This will remove any overclocks you have currently set for CPU/RAM.

This should be the first thing you attempt – it has been generally accepted as the 'quickest' way to fix this problem for a lot of users. It didn't solve it for me but it was a step in the right direction. Here is a diagram of what to do:


By the way, this has been taken from the manual.
 
Change the 'APM'
This appears to fix it for a lot of people too:

- Enter BIOS (spam F12 upon reboot) – Click on the 'Advanced BIOS' up the top right
- Go to 'Advanced' tab
- Go down to 'APM'
- Press Enter
- Enable the "Power on by PCIe", leave everything else as disabled.

Are you getting a message about the Marvel Controller not having any connected disk?
For those of you not using the Marvel Storage Controller, you may see this happen:

- Asus splash screen;
- Marvell boot hard drive screen;
- Asus splash screen;
- Marvell boot hard drive screen;
- Windows 7

If you're not using it, then you can turn it off by going to:

- Enter BIOS (spam F12 upon reboot) – Click on the 'Advanced BIOS' up the top right
- Go to 'Advanced' tab
- Go down to 'Onboard Devices Configuration'
- Turn Marvell Storage Controller to disabled

UPDATE THE BIOS TO THE LATEST VERSION

Updating the BIOS is not everyone's favourite thing to do. I know that when I do it I practically break out in to a cold sweat before hitting the "OK" button to get it started.

Firstly, you'll need to go to: http://www.asus.com/Motherboards/Intel_Socket_1155/P8P67_PRO/

Find the appropriate BIOS – personally I would never, ever, install Beta versions so I'd recommend getting the latest stable version.

Never flash BIOS through windows/software. It sucks and the last thing you want is a dead MOBO on your hands.

To Flash – find a guide on the net or us this rough one:

- Get a FAT32 USB Drive
- Put the .ROM on to the drive
- Reboot and enter into the BIOS
- Once in advanced bios, go to TOOL
- Select ASUS EZ Flash Utility
Don't freak out! Your screen may go black... gave me a heart-attack first time (lol)
- Find the drive and .ROM file you have and use that to flash. Follow any on screen prompts

 
Final two things that I had to change:
When you boot, you'll notice that the lights on the MOBO will go on and off. It goes in a sequence where it checks everything:

- CPU
- RAM
- VGA (graphics)
- Boot device (HDD)

If it gets stuck on any of these, then you may also be able to find your culprit for the double boot. When booting cold, the first time my box was getting stuck on a red VGA light. It would hang there, then reboot and work "fine". It was also crashing in DX11 games repeatedly.

I thought the card was boned but did a little more digging and found two things were wrong:

- My RAM slots needed to be changed
- My overclocking had somehow changed from X.M.P to 'Manual' and was unstable
I changed this back and then voila, problem fixed!

Any Questions??
I'm more than happy to help you trouble shoot your issues with the p8p67 PRO. It took me over the course of a few months here and there to actually sit there and nut it out. I thought I had it fixed but now I 100% know for sure it is fixed.

thanks dude good guide, hope it solves my problem

me too!

Probably best thing to do is try and figure out what is causing the double boot. Silly to say, but it could be the VGA light hanging? Or the RAM light hanging?

Or is it the marvel controller?

That way you might be able to save yourself some time.