If there is any chance that you guys installing windows 7 while in IDE mode for your SATA drives (just like me) and now want to change it to AHCI mode in the bios only to get windows startup crash, here is the step.
in the BIOS, change back the SATA mode to IDE, start windows normally and do below step :
1. start "Regedit"
2. Go to : HKEY_LOCAL_MACHINE / SYSTEM / CurrentControlset / Services
3. Open msahci
4. In the right field double click on "start".
5. In the value Data field enter "0" and click "ok"
6. exit "Regedit"
restart your PC, back to BIOS again, and change the SATA mode to AHCI, your windows should start without any problem.