error installing windows 7 in Notebook Asus X451CA or X451C

1. backup your file on your note book using bootable or another tools backup
2. prepare your windows 7 installation disk or usb installer 
3. remove all partition on your notebook drive (important) if you just format system partition its doesn't works because windows 8 last partition has protect to lock the system
4. make new partition for system
5. next for install
6. enjoy this trick
or see this article here