Hi Alif,
have you tried to use the particular SD-card with another OS (e.g., Linux) installed? Not all SD-cards work with the Pandaboard. If you don't even see the output of the U-Boot boot loader, there must be something wrong with either the SD-card or the serial connection.
Have you tried to connect a HDMI display to the Pandaboard? The scenario installed in the disk image contains a GUI. So even if the serial connection does not work or minicom is misconfigured (your settings look fine to me though), it would display something on screen.
Best regards Norman