Nissan Repair: Over drive system ., nissan repair, car moves

Question
i have nissan sunny model 2001 , suffering from a problem with over drive system , where the O/D lamp blanks on and off several time when operating the car , at the same time the car does not move automatically when transmitting to "D" from the stationary state and it needs to kick down the benzene pedal , and car moves at 70 KPH at 3000 RPM .. they couldnt find out the problem at the maintenance center.

Answer
well, if you took this to a shop and they couldnt find the problem i dont know how much help i can be across the sea.  the only 2 things i can think of to help you would be its either the automatic transmission computer, which is located under the dash, or its the transmission itself, which was my first guess when reading your question.  take the car to a qualified nissan repair shop for a better diagnostics.