Hi Kushal,
This is very easy to tackle. When you boot your system, go to the
system setup(The BIOS setup by pressing del on some systems and F8 on
some others, but check that on your system) Once your enter the BIOS
setup of the system, there are options for setting a BIOS level
password. If you set up a password here, then every time your system
boots, it will prompt for a password before loading any operating
systems... Hope this reply is of help to you.....
cheers and regards,
Krishna Bharadwaj