Ideally you should have set the BIOS to AHCI mode BEFORE installing Windows. Now that it's already installed switching the mode causes it to crash because it doesn't have the correct drivers loaded. But there is a way to switch modes without having to reinstall Windows:
1) Run the Registry Editor (regedit.exe)
2) Navigate to Registry Key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci
3) Set the "Start" value to 0 (zero)
4) Navigate to Registry Key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Pciide
5) Set the "Start" value to 0 (zero)
6) Shut down
7) Start up again, but before Windows boots go into the BIOS configuration screens and change the disk mode to "AHCI". Save the new BIOS configuration and restart so that Windows boots.
When Windows starts, it will detect the change, load new disk drivers, and do one more reboot to start up with them.