Long menstrual cycles (lasting longer than 35 days) may sometimes, although not always, affect your ability to get pregnant. Efforts may simply take longer, because you have fewer chances for conception within a year (ovulation occurs less frequently). That's why it's highly recommended to keep an ovulation calendar, so you can pinpoint ovulation accurately. It's also important to check if ovulation occurs, because long cycles are more often unovulatory.
In long cycles, delayed ovulation may be a problem. Usually ovulation occurs about 14 days before the next period. In a 36-day cycle, for example, ovulation happens more or less on the 22nd day of the cycle. Delayed ovulation may be associated with inferior egg quality, which may affect its ability to get fertilized.
Of course, there are many women who have long cycles and become pregnant without any problems. If, however, you have been trying to get pregnant for some time and your cycles are longer than 35 days, you should consult your doctor.