Hi,
you ned to have updated the Nvidia driver to the latest version with a clean install, and download and install c4doctane 2020.1.5-R4, to have the first version supporting new Ampere RTX 30X0 GPUs.
Unfortunately, AI Denoiser cannot be active in the scene, or the render never stops, since it is not supported in 2020.1.5 SDK with RTX 30X0 GPUs.
You need a version based on new 2020.2 SDK, based on new cuDNN library, to have the first version supporting RTX 30X0 GPUs correctly. At the moment we are at 2020.2-RC4, so very close to the final version:
viewtopic.php?f=33&t=76451In the meantime, if you need to render with AI Denoiser active, you should need to use a 2020.1.5-R4 plugin, to export your scene to Standalone 2020.2-RC4 in .orbx format and render from there.
ciao Beppe