title: My Anaconda stopped working all of a sudden
body: <p>My Anaconda stopped working after I installed some packages for statistics (not entirely sure if it is related), I cannot open Jupyter Notebook or Spyder, I can only open Anaconda navigator from the Anaconda command prompt and once there, if I try to run Jupyter or Spyder I get this error message:</p>
  
  <pre><code>`Traceback (most recent call last):
  File "C:\ProgramData\Anaconda3\lib\site-packages\jupyterlab_server\server.py", line 20, in 
  from notebook.notebookapp import aliases, flags, NotebookApp as ServerApp
  File "C:\Users\Jorge87\AppData\Roaming\Python\Python37\site-packages\notebook\notebookapp.py", line 49, in 
  from zmq.eventloop import ioloop
  File "C:\Users\Jorge87\AppData\Roaming\Python\Python37\site-packages\zmq\__init__.py", line 47, in 
  from zmq import backend
  File "C:\Users\Jorge87\AppData\Roaming\Python\Python37\site-packages\zmq\backend\__init__.py", line 40, in 
  reraise(*exc_info)
  File "C:\Users\Jorge87\AppData\Roaming\Python\Python37\site-packages\zmq\utils\sixcerpt.py", line 34, in reraise
  raise value
  File "C:\Users\Jorge87\AppData\Roaming\Python\Python37\site-packages\zmq\backend\__init__.py", line 27, in 
  _ns = select_backend(first)
  File "C:\Users\Jorge87\AppData\Roaming\Python\Python37\site-packages\zmq\backend\select.py", line 28, in select_backend
  mod = __import__(name, fromlist=public_api)
  File "C:\Users\Jorge87\AppData\Roaming\Python\Python37\site-packages\zmq\backend\cython\__init__.py", line 6, in 
  from . import (constants, error, message, context,
  ImportError: cannot import name 'constants' from 'zmq.backend.cython' (C:\Users\Jorge87\AppData\Roaming\Python\Python37\site-packages\zmq\backend\cython\__init__.py)
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
  File "C:\ProgramData\Anaconda3\Scripts\jupyter-lab-script.py", line 5, in 
  from jupyterlab.labapp import main
  File "C:\ProgramData\Anaconda3\lib\site-packages\jupyterlab\labapp.py", line 14, in 
  from jupyterlab_server import slugify, WORKSPACE_EXTENSION
  File "C:\ProgramData\Anaconda3\lib\site-packages\jupyterlab_server\__init__.py", line 4, in 
  from .app import LabServerApp
  File "C:\ProgramData\Anaconda3\lib\site-packages\jupyterlab_server\app.py", line 9, in 
  from .server import ServerApp
  File "C:\ProgramData\Anaconda3\lib\site-packages\jupyterlab_server\server.py", line 26, in 
  from jupyter_server.base.handlers import ( # noqa
  ModuleNotFoundError: No module named 'jupyter_server'
  `
  </code></pre>
  
  <p>I tried uninstalling Python and installing it again, I tried also uninstalling Anaconda and installing it again but nothing seems to work.</p>
  
  <p>I also tried updating Anaconda and writing the command 'Activate Root' and then 'conda update' as I saw in other solutions in stack overflow but nothing seems to work.</p>
  
  <p>I´m using Windows in case this is relevant.</p>