I have tested the USB in another computer. It works fine there. Seems to be some problem with the laptop.
I used Universal USB Installer to write Ubuntu 14.04.1 in my USB.
I am using latest BIOS driver.
I have changed BIOS settings appropriately (screenshot attached).
I have tried both NTFS and FAT32 file systems. In FAT32, the USB is not at all shown. While in NTFS, when I select the boot device, it starts Windows 8.1 again.
I have also seen the solution for UEFI based laptops. It did not work for me.
Legacy Support is enabled.
Secure Boot is disabled.
Please help somebody.