If you have installed Windows 7 with IDE mode then, you want to change to AHCI, some BSOD (Blue Screen of Death) will appear.
Changing from IDE to AHCI is a good thing. You will experience a slight increase in booting time and some other HDD related performances.
To avoid the BSOD during the Windows 7 boot, you can edit the DWORD value in the Registry Editor. Please refer to the image above.
You can download the .REG file here, extract it, double-click and restart.
Don't forget to change your HDD mode to AHCI in BIOS Setting too.
p/s: According to ASUS a BSOD could also occur due to shared/non-dedicated SATA power cable.