NOKIA N70M
Screen vanishes all of a sudden

Sir/Madam

I purchased my N70M Nokia Mobil last year in May and everything was fine a few days back. 4-5 days back my mobile's screen vanished and i could see only white screen. Nothing was visible but phone was otherwise working i.e incoming was ok. Once in a while the screen comes back and the phone works as if nothing had happened. But all of a sudden it vanishes after sometime may be 10-15 minutes or 1-2 hrs. What could be the problem. I am at Nazira, Dist-Sivasagar, Assam. Kindly reply as soon as possible. Regards.