There could be several reasons:
most new BIOS have a one time boot menu. The BIOS should show a few options during POST. (Mostly you have to press F12 or F11)
If your BIOS doesn't support this, change the Boot order (F2 or DEL to enter the BIOS setup)
Next ensure the disc is finalized. If it is not, it might be possible that your PC ignores it on startup.
Burn the CD again with a slower write speed, 4x or 8x (DCD); 8x or 12x (CD) should be fine.
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Be careful with DBAN. It wipes every(!) connected storage device (SSD, HDD, USB stick...) without any warning and starts to wipe all devices at the same time. There is no way back. (sure you can shutdown the computer, but not without data loss)
Depending on the wipe method, it is impossible to recover the data.