When is a good is a good time pregnant your wife

 One of the best ways to get pregnant to determine approximately what time each month that you do ovulate. The best way to do that is to get a basal body thermometer and chart your temperature each morning upon waking, before doing anything else. If you do this for some time you will see that your temperatures rise each month a few tenths of a degree and then stay up until your period comes. This shift in temperatures signifies that you have indeed ovulated. Once you have a good idea when this occurs month to month, you will have a better chance of predicting when you might be ovulating.

It is important to note, the best way to get pregnant is to make sure the sperm is "waiting" before the egg is released. The sperm can live for approximately 3-5 days inside a woman, but the egg only lives for about 12-24 hours. So, for the best chance of conceiving, it is best to time intercourse for several days leading up to ovulation and on the day of ovulation too.

I totally agree with that you must follow the biological signs

In addition, this seems like a good website for How to know when you're ovulating. 

Wait a week after her period then keep going at it until her next period

Have you checked whether your sperm is viable? If you've been trying for months with no success, there's obviously something going on. To put it in perspective, there is a major issue in North America of one-night stands resulting in pregnancies, a lot of 1 for 1's out there.