I have gone through the issue which you are facing with Nokia PC suite and Nokia C5-03 mobile phone. I would like to ask you first about which you version of Nokia PC suite are you are using? If you are using old version of Nokia PC suite then I will suggest you to first download latest Nokia PC suite and then install that in your computer. now after installing latest Nokia PC suite you have to check whether your problem get solved or not.
As far as I know after trying this solution your problem will get solved.