I will write a remedy for impotency from Lal Kitab in this post. Please note this remedy is for those men who don't have enough sperms in their semen to produce children.
Lal Kitab says that when Venus is in 11th house native does not have sufficient sperms in his semen to produce children. There are other combinations in the horoscope as well which may make a person impotent but the stress in this post is not on the combinations for impotency but on the remedy for impotency.
The remedy to be done in this case is as follows:
Take a pure gold rod and milk in a glass. Heat the gold rod in fire, when it is red hot dip it in milk. Now heat the rod again till its red hot and dip it in milk again. Repeat this process for eleven times. Drink the milk now. It will produce sperms in your semen and empower you to produce children. Keep on doing this remedy regularly.
Please note that this is a general remedy and more specific remedies can be suggested after looking at horoscope.