Nokia C7 display problem

I have a Nokia C7.My problem is when i received a call or after dailing a number and i press the call button,the whole phone display go blank.Anyone can tell me what is the problem?

Well I think you need to Hard Reset your mobile phone and you ll lose your data. Before going ahead with this I will suggest you to visit to the nearest Nokia Service Center. Explain them all your porblem they might able to fix your phone.

Thanks.what do you meant by hard reset?Do you mean reformat the phone and reset to factory setting?