When you come to open your developer console. It opens and starts to load but it quickly minimizes, showing a “loading…” text.
After that, the developer console’s window freezes completely, allowing you only to close it. Same happens to the window which opened the developer console (your Salesforce homepage)

Resolution

First, kudos to this author at https://salesforce.stackexchange.com/questions/80453/developer-console-is-not-loading

And here are steps in details:

Step 1:

Do GET in Workbench

Step 2:

mine is: 1de28000004VCFFAA4, so here is the full link to do GET:
/services/data/v39.0/tooling/sobjects/IDEWorkspace/1de28000004VCFFAA4

After that, do DELETE

Step 3:

After deletion, here is how it looks like:

And the Dev Console is back to nomal, if you’re lucky 🙂

Don’t forget to create another workspace since the current workspace has been deleted.

Happy forcing!