I manage to fix the problem.
Issue appears to be the SATA hard drive. By default it is attached to sda. It seems that rpiboot can't mount module anywhere else but sda.
Quick tutorial for those who prefer to install Computing Module using live CD (Linux Mint 17):
1. Disconnect all internal/External hard drives (leave CD/DVD/Blu Ray drive).
2. Make sure that J4 (USB SLAVE BOOT ENABLE) is set to the 'EN' position
3. Make sure Jumpers on J3 are set to 3V3 or 1V8.
4. Boot from CD Linux Mint 17.
5. Launch Xterm.
6. Set date:
sudo date MMDDhhmm
7. Set tools required:
sudo apt-get install git
sudo apt-get install build-essential
sudo apt-get install libusb-1.0-0-dev
8. Make it nice and tidy:
9. Download rpiboot:
git clone --depth=1 https://github.com/raspberrypi/tools
10. Connect USB Cable to your computer and port J15 (USB SLAVE)
11. Connect USB Power cable.
12. Check where CM is:
13. Copy file to the folder RaspPi (Drag and Drop) from external USB device or download from http://downloads.raspberrypi.org/raspbian_latest
14. Extract ZIP file (Right-Click -> Extract Here).
15. In Terminal, navigate where IMG file is or open new terminal window and type cd Desktop/RaspPi
16. Flash the image:
sudo dd if=raw_os_image_of_your_choice.img of=/dev/sda bs=4MiB
17. When Finished, Unplug microUSB from J15 (USB SLAVE)
18. Set J4 to disable (DIS).
19. Unplug and plug back in (cycle) the microUSB power (POWER IN)