I have armed my esc once with the kkv 2.1.5 board but after that the screen got blank and no text or any sound is coming. What could be the problem and how to solve it ? Please answer it asap...

Try to arm again
If its armed n worked fine then ur  display is broken or has connection issue

I can try that..but there is no sound or display. ..so I won't be able to find whether it is armed or not

Possible cause-
95% wrong connection( only white light, Nothing written.I had same problem when i build my first quad with kk2.0)
2% broken screen.
2% change receiver(i had some problem while arming. Just changed receiver and it worked!)
1% unknown

I used multimeter to check whether the connection between the output pin's positive and negative..only one of them is working.what now ? Any solutions ?

check this image and compare to yours.
or first of all remove all connections and only insert motor 1 esc wire in right top of board as shown in image.