I have flashed an ISO to a USB, restarted my computer and selected the USB as the boot option. The screen flashed to black and then the boot option menu came up again. After selecting the USB option for the second time and computer boots directly to windows as if that was the option I chose.
I used Rufus to flash the ISO. My computer can boot from a USB with a Linux ISO but this particular ISO is for DBAN.
Your PC is currently set to only boot using UEFI (because Secure Boot was enabled). However, the USB drive you have is not UEFI-bootable – it does not contain the required files.
Depending on how new your PC is, you may be able to switch to Legacy booting (sometimes also called BIOS booting or “CSM”). Don’t forget to turn it off again afterwards. The switch is usually located in the “Boot” section of the firmware setup.
If your PC is very new, it’s possible that it doesn’t support legacy booting at all. In that case, you won’t be able to use DBAN.
Now, on DBAN:
Using DBAN is almost always not necessary. Modern hard drives usually cannot be restored by forensic methods even after a single random wipe. (Reference) This can be easily accomplished using any modern Linux distribution:
dd if=/dev/urandom of=/dev/sdX bs=4096.
On a SSD, wiping isn’t truly effective. Instead, you should use the drive’s built-in Secure Erase facility, if available. If there is none,
TRIM the entire device. Only if none of these methods is available should you overwrite it.