Follow the steps to boot from your pen drive(USB):
First of all make a boot-able pen drive (To see how to do it click --> http://aimonsoft.blogspot.com/2010/08/use-pendrive-to-install-operating.html )
1)Insert your boot-able pen drive.
2) Restart your computer.
3) Press F2 when your computer boots.
or
press the option for "Boot options" (it will be either f8 or F12)
4) In the "Boot sequence order" , make "USB/Flash drive" as the first drive to boot from.
5)Your computer boots from your USB-Drive(pen drive).
------------------------------------------------------------------------------------------------------
Tags: How to boot from a pen drive How to change the boot order How to change the boot sequence Make a bootable pen drive Change your boot sequence order