I also have a new WD HDD on which I've now installed Win7.
If I connect the old drive prior to booting, it shows up in the BIOS, but as PATA. I've tried booting from that drive under ACHP, IDE and RAID but after the Windows load screen it has a BSOD (probably due to old MB drivers?).
If I boot from the new HDD the Windows load screen just keeps going.
If I don't boot with the old HDD connected, but put it in the Hot Swap afterwards, there's still nothing happening. The first time it failed at installing the drivers. Now it shows up in Device Manager as "Disk Drive" and has the latest drivers installed. It does not show up in Disk Management, so I can't simply map it either.
It's a sata drive, strangly enough listed as pata and when I hook them both up and boot the new one the Windows load screen just keeps going on and on... I'm going to make it external tonight, but if I format it after getting the data will it be able to work then? Because I would very much like to use the old one for the OS and the new one just for data.
You may have corrupted the old HDD partitions in that it now does not show up in disk management. With both the new, and the old hot swapped in, go to disk management, and upload a screenshot of Disk Management dialog box, expecially the lower graphical area.
That way we can see exactly what is seen by the Win-7 OS.
If you can copy off the files from the Old drive, then you can delete all partitions, back to Unallocated Space, and repartition and reformat it. However if you are going to put the Pri Win-7 OS on it, should do that as a Clean install of Win-7, using the custom install, and remove all partitions there.
Even if you have an OS on a secondary drive, if you connect the Primary OS drive in the SATA_0 port, with this set first in the boot order, and the Secondary OS as SATA_1 or SATA_2, it should not read the MBR of the secondary drive.
If there were still a problem, the using DiskPart to remove the Active Flag from the Secondary Drive would make it not be pointed to from the EFI MB interface.