Installing packages problem with Anaconda Navigator

I have problems installing packages in the Anaconda Navigator. When I install a single packages, for example, the requests package (which was marked as updateable), the window “Update Packages / The following packages will be modified:” pops up, but no packages are listed. The list is blank and nothing happens. This also happens, when I try to update another package. The window stays blank and the only thing I can do is cancel the update process (close the window).

I also tried to update the whole Anaconda installation via conda update anaconda. This also seems not to work: “Solving environment” shows up for more more than an hour. Even if I reboot my computer (it’s a Dell Latitude Notebook and I have Windows 10 Enterprise installed).

What could be the problem and what would be an appropriate solution?