I am on a Mac and the emulator is not working. I am teaching a course and the students are on a Windows computer and cannot get the emulator to work. It says on the screen that is loading and it never loads and comes up. Do you have any ideas of what might be the issue? All of use are using google chrome and we all have different computers. None of us can open an emulator. We downloaded and installed it successfully. Any ideas are appreciated.
Start with the school setup article
Welcome Robyn
- are you all using the school network? A possibility is your IT department is blocking a port or is not white listing a necessary MIT link.
Share this information with your school IT person
School IT/Network Admins: Information specific to school networks This is the same link ABG recommended you try.
The key areas that need to be white listed are:
Also note that
Emulator — Updating AI2 Companion
Just as the physical device uses the AI2 Companion app to support live development, the emulator requires a copy of the companion installed. The App Inventor setup tools install a “place holder” version of Companion when they install the emulator. Unfortunately, this version of the Companion will be out of date due to new releases of MIT App Inventor since the setup tools were created. Accordingly, the first time a user uses the emulator, not only is the Appinventor-emulator-data copied, but the user is prompted to upgrade the emulator’s Companion software. If you do not respond positively to the pop-up instructions that appear, the Companion will not update. Running App Inventor without the updated Companion may cause coding problems for the user.
The updating mechanism requires that the emulator.exe program be able to make outgoing requests to ai2.appinventor.mit.edu and code.appinventor.mit.edu. When these connections occur, the emulator will download an updated companion app with the filename Emulator.apk. This will be installed over the existing companion version bundled with the emulator. Note that because the emulator data is copied per user, every person will need to run the update to get the new features.
It is possible that everyone's emulator will work if they take their PC or Mac home and use it on their home network? Has anyone in the class done this? Your home network shouldn't have any ports that are not white listed. 
Also, which Connect-> sequence to you use from your Project to connect to the emulator?
My students use the AI starter then they go to connect and click on emulator. However, when the window comes up and you see code running, it fails. They did not see the update option pop up.
Here's how to manually update the Companion in an emulator:
(from the aforesaid FAQ)
Thankyou this was helpful.