There are various ways to ascertain the impotency and in astrology texts there many yoga are described for such a birth. Sign and Planets both are important in this regard. Sixth house affliction, affliction of Mars and impotent planets, their position and nakshatra are taken into consideration. Someone may not be impotent with regard to erectility but he may be impotent with regard to reproduction or progeny. Basing on the nature of sign and planets there are few combination which makes one impotent.

Let us see one combination in this chart of Karan Johar..
If lagan is odd sign, Moon is in odd sign or in masculine sign, Venus in odd sign/masculine sign or afflicted by masculine fiery planets Sun/Mars then there will be impotency. Here lagan is Leo, Moon is in Libra, Venus in masculine sign with Mars. His time is unknown therefore navansha can’t bee seen. The combination is seen from Navansha too.

Let us see another Chart of Salman Khan..

If lagan is odd sign and Moon is in odd sign and Mars sitting in even sign aspects lagan then impotency is possible. Here Moon is with impotent planet also and Venus in 10th house. In Navansha also Moon and Venus is in masculine sign and Mars is in 6th house of disease with impotent planet.

Let us see third chart of Javed Akhtar

lagan is odd sign and Moon-Venus is in odd sign and lagan lord is with impotent planet who is 6th lord in odd sign aspected by impotent planet. Time is not known so navansha can’t be seen but above combination is sufficient to make him impotent.