that after accessing the BIOS you set the CD /DVD as the first boot device and SAVE the setting? That boot manager missing makes it look like your first boot device is still the hard drive.
If you are certain that the DVD is the first boot device have you tried a Linux distro on CD (rather than just on USB)?
I am asking because I have been known to forget to SAVE the changed boot device sequence once in a while when tired or had other things on my mind.
Alienware M15X. Last known config was BIOS A09 and Windows 7 Ult (was working for ~3 years).
Ran into some serious boot errors the other week, so I wiped the drive and reset the BIOS, but when I boot it loads the POST screen, then gives me a "BOOTMGR missing\nPress CTRL-ALT-DEL to restart" error message. If I put in the recovery DVD on boot, it gets ignored (even on subsequent boots). If I put in a boot USB (tried Win7, Win8, and several Linux Live USBs), the boot freezes at the POST screen and pressing F2 results in a *BEEP* then nothing, and F12 does nothing.
A friend of mine insists this is a software issue.