If you installed Windows Vista or Windows 7 in IDE Mode you can't just change the SATA controller to AHCI Mode. As you may have discovered, this will result in a BSOD and the PC will just reboot. This is due to the way that Windows is installed but you can change to AHCI Mode without reinstalling the OS though, so all is not lost. But it requires a registry tweak to get things working properly.
AHCI stand for Advance Host Controller Interface. AHCI is a hardware mechanism that allows software to communicate with Serial ATA (SATA) devices (such as host bus adapters) that are designed to offer features not offered by Parallel ATA (PATA) controllers, such as:
• Hot-Plugging
• Native Command Queuing (NCQ) -might improve computer/system/hard disk responsiveness, especially in multi-tasking environment
• If you are running an SSD then AHCI passes the TRIM commands to the drive to keep it clean and healthy.
The detailed steps from Microsoft website for switching to AHCI Mode after an IDE install are as follows:
• Exit all Windows-based programs.
• Press [Win] + R or take the RUN option from the start menu.
• Now type regedit there and press Enter Key to open up the Registry Editor Window.
• If you receive the User Account Control dialog box, click Continue.
• Locate and then click the following registry subkey: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\msahci
The menu here is quite long and you have to scroll down the list about halfway to find what you're looking for.
• In the right pane, right-click Start in the Name column, and then click Modify.
• In the Value data box, type 0 [3 is default], and then click OK.
• On the File menu, click Exit to close Registry Editor.
• Restart your computer
• Go to BIOS and enable AHCI, Save & Reboot
• Another restart will be required to finish the driver installation.
If you are running Windows XP things are a little trickier but here is a really useful guide that shows you the steps you need to take:
http://www.bootbeta.com/blog/guide-enable-ahci-in-windows-xp-after-installation.htmlEDIT: 24/01/2013To change Windows 8 from IDE to AHCI Mode check here:
http://forum.giga-byte.co.uk/index.php/topic,6721.msg78596.html#msg78596