window doesn't usually control that feature, sometimes certain programs INSIDE windows may do it, but usually it stems from moves made in the BIOS.
your easiest procedure to undo things in the bios is to reset it. find the "clear cmos" button or jumper that is physically on the mobo pcb, and while the computer is off hold it in for ten to 15 seconds. that should completely erase whatever settings were once held in there. it'll be a clean start. I am not completely familiar with your board, so read the manual on exactly the correct method of doing this, but generally that is how it is done.
you should familiarize yourself with the current settings before you do the clear, though... there'll be some other stuff you might want back, most importantly the setting on the boot and hdd order and the sata controller... whether it is in IDE, RAID, or AHCI mode. best is RAID mode, as it is inclusive of AHCI, and gives you some bells and whisltes the IDE mode won't give you. BUT if your OS was installed in IDE mode, it is probable that what you installed as your OS won't read in any other mode. this arises from not having installed any driver for the sata controller when you did the original install. that is the reason for IDE mode, simplicity at OS install.
sometimes these boards have different controllers for one reason or another, so watch for that too. i know that there is both intel and marvell controllers on many asus boards, and who knows which controller you are using for the OS? you should make sure to know this.
my main rig...
asrock 970 extreme3
AMD athlonII X3 440
zalman cpns5x performa hs/fan
crucial ballistix 2x4gb sport ddr3-1333
powercolor ax7750 1GBK3-H vga
antec neo he 650r
Samsung 840 EVo SSD 120 GB
toshiba 2TB HDD 64M cache sata3
seagate 1TB HDD 64M cache sata3
hitachi 2TB HDD 64M cache sata3
lg wh14ns40 bd burner
optiarc ad-7240s sata dvdrw (nec chipset)