File "/usr/lib/python3.5/asyncio/base_events.py", line 340, in run_forever
raise RuntimeError('Event loop is running.')
RuntimeError: Event loop is running.
After some time searching for solution on Google, here is what I found: I simply need to re-install some of the jupyter-related packages.
$ pip uninstall ipykernel ipython jupyter_client jupyter_core traitlets ipython_genutils -y
$ pip install ipykernel ipython jupyter_client jupyter_core traitlets ipython_genutils
Now, the jupyter notebook runs just fine. I suppose the problem was that I installed some packages that somehow interfered with the already-installed jupyter related packages above and caused the error. After removing and re-installing the jupyter-related packages, jupyter finally seems to run just fine!