No bootable device found ( Install windows on Mac ) I'm owning a macbook pro 13 inch mid 2009 and a USB thumb drive Kingston DataTraveler 100G3 16 GB.

I successfully installed Windows 7 on my Mac using Bootcamp ( with a little trick to enable "Creat a bootable flash drive" feature which was hidden in my bootcamp version ).

The problem is, after about 1 month, I followed exactly the same procedure, with the same USB and ISO installation file on my friend's computer ( Macbook Early 2008 model ), it just didn't work. When I tried to boot into USB, it said : "No bootable device - insert boot disk and press any key ". Similar to this video : https://www.youtube.com/watch?v=NgWBY6IezQA

And to be even more frustrating, I tested it on my computer again to check whether there was something wrong with my friend's computer, my computer couldn't even boot into the USB again

I'm really desperate now. I feel like there is some mysterious thing going around here. My USB's working perfectly otherwise.
The problem is that your MacBook doesn't have BIOS, it uses EFI instead. I won't go into the differences between the two, but the Boot record you've created on your USB is for BIOS not EFI.

There are two fix this, one requires a PC with Windows, the other doesn't. 

Windows method:
Go to this link: http://www.eightforums.com/tutorials/15458-uefi-bootable-usb-flash-drive-create-windows.html

It'll explain the steps you need to follow to have your MBP boot from the USB.

Other method:
Go to http://gparted.org
Download and run GPARTED
Convert your MBR volume to GPT

Now you're EFI will recognise your USB as a bootable device :)