Ovarian drilling done at day 4 of my cycle. i had a positive ovulation test on day 16. is it possible despite positive test ovulation doesn't occur?

It is possible: It is possible that despite a change in hormones (i.e. positive ovulation test) there is no mature egg that gets released. The best way to assess that would be by ultrasound. Good luck!

Ovulation: I assume that you were using a urine ovulation predictor kit. These kits detect the LH surge which occurs prior to ovulation and are good at doing that. There are some false positive tests. However, if you were testing on consecutive days and it went from negative on a couple days to positive then most likely it is a preovulatory surge of LH.