The videos embedded in the lessons are standard .mp4 files. If you can/could play one, then you should be able to play them all. But sometimes something goes wrong...
 
Our course hosting platform is Teachable. They updated some security elements that may conflict with some browsers. In the settings, look at the settings for “Privacy, search and services” and then “Tracking Prevention”. If you are using “Strict”, adding “https://www.iamtimcorey.com” as an exception and restarting the browser will allow video playback. This may vary by browser type
 
If that did not help, let's start by using standard debugging steps: identify the scope and clarify the specific error.
  • Scope - Is the problem related to loading one specific lesson or loading the course? Can you access another course in your account? Can you watch a video you already watched before? Here is a link to a lesson preview video, does it play? How about this YouTube video? Do the videos play in a different browser?
  • Error - If you are getting a specific error message, search the internet for possible resolutions by searching for the message.  

If the problem is that YouTube or the lesson videos will not play, then you likely need to try basic system cleanup efforts. Consider these steps:

  • CTRL+Shift+R in the browser to force a full-page reload
  • clear cache
  • restart the machine
  • free up space by clearing temp files
  • Make sure your system and browser versions are up to date

This page may help - 25 vital computer maintenance tips and checklist to protect your device | NortonLifeLock

If you are having problems getting into a new course, check out this article - Why can't I log into IAmTimCorey?

I don't know if this will help much but it is what our host system Teachable offers - Troubleshooting Course Issues – Teachable. 

One last possibility to consider, Teachable sometimes pushes updates to their system. You may just need to step away for a bit and try again later. We have had users try everything above, walk away frustrated and when they return, all is working. You can contact Teachable support directly at support@teachable.zendesk.com. 

If you are still having trouble, contact us at Help@iamtimcorey.com. Please include screen captures and as much detail as you can about the scope and error you are getting. Also, please include what you have already tried when attempting to resolve it.