I have a windows 8 system in which it started saying, "No bootable device found" but when I go into the boot it shows the HDD there. I have no idea what should I do. I already took it out and put it back millions times.
You may have a hard disk error or some corruption of the drive paritions involved in booting. If you have a Windows install disk try booting from it and running a disk repair. (You may need to go into the BIOS to change your boot device priorities) to enable boot from the optical drive.