Might help might not. Rule of thumb is new mobo and or new cpu it is best to do a fresh os install. Sounds like you have built a new rig and are trying to go easy and just pop in your old drives with os installed from your old system and go. That might not work. Some say it is ok and works fine if just pop in a cpu upgrade or maybe a alike mobo etc. You should understand the mobos and cpu's are different and different drivers etc from the last mobo and os install. Quick or lazy is not always the best. Not trying to give ya a hard time or any thing- just saying is all. 775 and 1155 is a large jump and way different mobos.. I really do not think you can skip a fresh os install. Maybe I misunderstand what you are saying- I am sorry if so.
As for which drive is your os drive normally it is the drive plugged into your #1 port on your mobo sata1 etc. Unless when you installed the os you had it install to another drive or not on the #1 port on your mobo. You can try and test them one at a time by unplugging one and try if no good un plug it and try the other.
** As a fact you might figure it out fast- Boot with the windows disc in the drive like you want to install the os- windows will say if the drive you are trying to install to already has the old os installed on it- Bamb! its figured out. It will not say the same thing for your storage drive - well not unless you was running a dual boot os system and 1 os on 1 drive and the other on the other. If you have the old os drive in and is what windows says the old os is on- you can go from there with a fresh install or just hit your reset button or something or turn off the psu button. I do not think the install disc will let ya just back out. Restart the system and remove the disc while it is doing so- if you are not ready to reinstall the os- or trying to read more and figure out what you need or want to do.. It should tell ya fast tho which drive is which.
Best I know the bios only lists all drives as udma #? ata/ ide drives- the bios does not say sata drive etc. None of my bios have any way and can be confusing. The bios will list the drive as boot device maybe or you have to set the boot order like the other fella said. Or drives might show under ide/raid or ahci/raid areas of the bios or ports [interfaces they are plugged into]- but do not actually say if the drives are ide or sata. No bios on any of my systems any way.. You know a ide drive can not be plugged into a sata port or vis versa. It can be confusing. Ha ha I am sure I can be confusing too. I am just trying to add all the info I can..
Mobos default to ide mode and is so you can pop in any hdd drive and get it up and running fast. If using sata drives ahci is the proper mode and you have to manually change it in the bios before os install or you can do a reg tweak after os install. Neither is hard to do. Some mobo manuals are better than others and will tell ya how to set up the mobo for ahci support- it is normally only 2 places in the bios you have to check or change.
AHCI may not be needed to get the system running- Some newer hdd drives or ssd might not work at all or will give ya fits unless it is set up in ahci support. You may not feel you need the added features of ahci but your sata drives will not run at full speeds unless set up in ahci and you do not need a raid to use ahci.
Different mobos and bios are not the same- so I can not tell ya how to enable it on your mobo- the manual or the mobo home site forums them folks can tell ya fast..
My guess is- your new mobo and cpu wants you to reinstall the os freash or it is not going to work. If so Figure out which was your os drive in the other system and plug only it in and reinstall the os. After it is up and running plug in your other drive.. If you can not figure that out or no other system you can try the drives in to at least figure which is the second or storage drive. You might get pissed and have to pick one and have to reformat it to install the os and lose all info on it. If you have to do that- I would pick the largest or fastest drive as the os or c: drive. After it is up and running and if you picked wrong- the other drive will be the last os drive and you have to reformat it for your storage drive on your new system.
I always mark and or install my drives in my system so I know which is which and know what ports on the mobo I plug them into and so not to have like probs you are having now.. I always put my os drive lower in the hdd rack so it is a lil more cooler than my upper storage drive. I normally mark them with perm marker 1 or 2 etc. 1 being my os drive. I might even mark the cables so it is easy to connect them when tons of wires are laying around in the system. Wire/cable 1 plugged into #1 port on the mobo etc- sata1 ide1 etc. Normally if running both ide and sata hdd the ide will be default 1/ or c: or main drive unless you change the boot order. That is more than likely because ide came out before sata drives did. A and b is normally fdd- d is normally a opti drive and e: is storage.
Could be another prob when your last mobo died it carried your os drive with it. Normally the only 1 thing in your system that can kill everything else is the psu. A bad psu can mess it all up.. Are you sure the last mobo was bad and not the hdd with the os on it? I guess you figured all of that out first- so..
You also need to know the proper interface for your hdd's sata or sataII etc and plug them into the proper ports on the mobo.
Sorry I can not help more- I do hope to have helped some. Hope you get it like it should be soon and you are happy with it.. Them p67 mobos and cpu's are awesome- Ya I think the 1155 is the p67's? 1156 is the p55 if I remember right?
Good luck- Take care..