The 1st thing that comes to mind is wether the boot order was changed to boot from USB devices. This is done by going into the laptops BIOS when the laptop is turned on. Usually by pressing a key ( delete, F1, etc.) Then go to the boot order section and make sure the 1st boot device is USB if at all available.
Next thing to note is that when .iso files are used to boot USB drives usually it has to be done through an application. Check out unetbootin
I have used it like 1 time but it worked very well and you can install a great number of linux distros with it.
Come to think of it, where in the world is my flash drive?!. . .