My phantom professional 3 had a damaged connection cable to the gimbal /camera .after installing the new cable i have no camera image being transmitted.
What can be the problem?  

Hello there. I am sorry to read and to know that you are having this issue with your DJI Phantom 3 Pro. Since this issue is happening on the said DJI drone I would recommend you to contact our DJI support team at https://www.dji.com/support?site=brandsite&from=nav for further assistance. Just a reminder that DJI do not recommend doing a DIY in fixing the said DJI drone to avoid further damaging the said unit. Thank you.