APM 2.x its a very old board.
nevertheless stil very popular, and most young boys get his first contact with Ardupilot comunity
because this APM... it has limited resources, yes, but very well used + is arduino mega based.
Piyush, you conected it via usb cable or via mavlink telemetry?
try better cable, maybe your telemetry is not sincroniced yet...
do this routine:
1st.- Connect via usb your apm
2nd.- Upload the firmware, via the MissionPlanner utility... you will se the last version available is 3.2.1 i think
but dont click the conect button just upload the firmware.
3rd.- wen is erased, dont touch the usb cable and click conect..
juts follow this : https://www.youtube.com/watch?v=30cCs4aHdB0&t=2s
in the very past, apm2.x firmware could be obtained juts by compiling the code in the arduino ide,
but now i dont know how to develop in this old APM...
now days, the users can modify and compile their own software on platforms like pixhawk, or just use
the mission planner utility or Qgroundcontrol etc
i think that if the apm have some whay to develop on it on todays, maybe more developers will join...