USB boot issue in windows7

BIOS Support
     The most fundamental go/no-go factor in using a bootable USB device is in the system BIOS (Basic Input/Output System). Either it will support USB booting, or it won't. If it does support USB booting, you'll probably have to enable the function, but that's relatively easy to do.

    First, check to see if your PC's BIOS supports USB booting at all: Do a full power-off restart of your system. As the PC wakes up, watch for text messages that briefly appear on screen. (If your PC normally shows a logo or other graphic at boot, try hitting the ESC key to reveal the text messages that the logo normally obscures.)

   Usually, the very first thing you'll see a message saying something like "Press DEL to enter SETUP." In some systems it's ESC, or a function key, or a key combination, instead of the DEL key; but virtually all systems announce some way to stop the boot process and enter the BIOS Setup program.


Different issues regarding USB boot which i faced.

1.Unable to boot in USB2,0 for the USB3.0 enabled system/laptop.
 
    I purchased a new HP laptop which is of 3.0 USB supported. I tried to boot via USB in that but its not at all accepting the pendrive for boot. I didnt get what actually is the reason behind this. I followed many steps and try to install windows xp also, though i face the same problem. At last i found the reason.
 In bios setup window, by default the USB3.0 is enabled so that its searching fot that type of USB. I disabled that and try to boot windows7 then it works fine.


2.Unable to boot using USB3.0 in the USB 2.0 enabled systems.

   We cannot able to boot using 3.0 usb in 2.0 enabled systems. But you can able to do the normal tasks like data transfer and all using 3.0 in 2.0 enabled systems.