Laptop will not boot BackTrack iso from USB

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http://www.backtrack-linux.org – I have recently used Unetbootin to create BackTrackR3-KDE-64 ISO on my USB pen. But when I reboot my laptop it does not boot Back Track. I have done the BIOS settings and moved all the USB options on my laptop to the top (USB CD, USB FDD, USB HDD), I have enabled Legagcy Kbd but still no luck. I have tried other backtrack ISO (BT5-GNOME-64, BT5-GNOME-32, BackTrackR3-KDE-32 but no luck as well. Everytime I create a new ISO on my USB, I tried it out on my Desktop (desktop USB has USB floppy, USB cd/dvd, USB hard disk option) and it works fine and boots in to backtrack. My laptop is samsung, runs (HowTos)