Firstly, make sure its not the selector swicth. You can check this by prodding a pen into the small hole at the lower part of the selector lever. If that works then you will need to replace the swicth which in my case was very cheap at my local garage. £12 for switch & £10 labour. If its the gear box 'goo' then I am not able to assist you because I havn't experienced that. 'Yet'. Hope this helps.