To create a bootable USB-stick:
Download the Recovery Image from the Knowledge Base. Check the md5 sum of the file before using it. If not correct, download again.
On a Windows PC open the ISO image with a proper program such as daemon tools.
The USB stick MUST be formatted with fat32.
Copy the content (not the ISO image) from the Recovery Image to a USB-stick.
Install bootloader on the USB drive, from command prompt in Windows. (Make sure you are running the command prompt as administrator in Win 7 above).
X:syslinux.exe --directory /boot/x86_64/loader --force --mbr --active X:
Replace X: with the drive letter the USB drive shows up as (DO NOT USE C:). If it seems like nothing happened, it is usually done.
A file named ldlinux.sysmay appear on the USB drive, that is normal.
The USB should now in theory be bootable.
When booting from USB: Select USB as boot device in BIOS.
A startup screen will show up: