The GPT-J model is quite big - the compact version of the model uses 16-bit floating point representation of the weights and is still 12 GB big. This means that in order to run inference on your computer, you would need to have a video card with at least 12 GB of video RAM. Alternatively, you can try to run the python implementations on the CPU, but that would probably not be very efficient as they are primarily optimized for running on a GPU (or at least this is my guess - I don't have much experience with python).