I shared my project with a friend and he couldnt start it, it just freezed after he clicked the green flag. Then I also tried opening the project in another tab and I got the same problem. You can click the green flag and the entire tab freezes, when you click the stop button after a few seconds it will stop trieng to run the project and you can interact with the code and everything. In the original tab everything works fine.
Welcome to the forum!
My first guess is that the original tab is running a different version of Snap!. Try clicking on the 
logo in the corner and choose About, and see what version it is.
Failing that, maybe after you saved the project you fixed a bug but didn't save again. Try saving (maybe under a new name) from the original tab and see if the resulting project is runnable.
I found a solution. After clicking every sprite in the project it can run