Error while burning bootloader
Based on this:

Note: The Arduino UNO stopped responding when I mistakenly
short-circuited a connection, I mistakenly passed 12v to one of the
header pins of sensor shield mounted on the board.

There are no I/O pins on the Arduino that are 12V tolerant.  You have almost certainly &quot;fried&quot; your Uno board.  It's possible the only casualty is the ATMega chip itself and replacements are available from a number of sources or you can purchase a &quot;raw&quot; one from an electronics reseller and use your programmer setup above to burn your own boot loader.
It's also quite likely that your sensor board is damaged as well.
From the Microchip datasheet:

You want something like this:
Adafruit Pre-programmed ATMega168p
Buy several, accidents happen!