What trouble are you having?
Which operating system?
I am using Windows Vista. I installed DNG convertor 8.3 but when I try to convert the NEF file it says the file is not recognised by the convertor
The D3300 requires DNG converter 8.4 or newer. That version of the DNG converter requires Windows 7 or newer. Lightroom isn't an option because it requires Windows 7 or newer. It looks like it's time for new computer.