PROBLEM: You have a pre-installed system running on a controller that is not set to RAID. You wish to switch your controller mode to RAID. (OR: you have a new controller that is RAID and a system that is not recognizing it). You may be getting "Bootmanager not found" errors or similar.
SOLUTION: You need to install the RAID drivers in your system. This can be done easily during a new system install but is slightly trickier if you have a pre-existing system -- see method below.
METHOD:
1. Retrieve your Windows install/rescue disk (or, in Windows 7, make a new one via Control Panel/System/Backup and Restore).
2. Locate and download the RAID drivers for your system and place them on floppy or USB drive. Shut down your computer.
3. Load the new controller or switch the controller setting to RAID.
4. Enter your BIOS and set the boot disk to your CD/DVD drive. Start using your resuce/Windows CD
5. The rescue CD can now be used to install the new drivers off the flash card.
6. Restart with your hard drive as the boot. DONE.
So as an example, which worked for me..
I have a ICH10 southbridge on an Asus mobo. I went to the Asus site and downloaded the RAID driver package. This included a utility that would set up a flash drive with the drivers (there is also a way to do this, per the mobo manual, via the BIOS). After loading a flash drive, I burned a Windows 7 rescue disk. I think restarted, entered the BIOS, switched my controller from IDE to RAID, switched my boot disk to the CDROM, and loaded the rescue CD. At one of the prompts, I selected "Load Third Party Drivers" and then used the flash drive to add them in. I restarted the computer off the hard drive and my system successful loaded.
This took me two days to figure out but once I came across the right solution, it was a very, very quick and easy fix!