You need Lightroom 5.6 or later.
As an alternative, you can download the FREE Adobe DNG Converter version 8.6 or later and use that to convert your RAWs to DNG, and then import the DNGs into Lightroom.
If that's not it, if you already have Lightroom 5.6 or later, please describe your problem in a lot more detail. What happens when you try to "open" (do you mean "Import"?) your photos? If there is an error message, please quote the exact complete unedited error message.
Thank you. Good information.