If a computation runs too long, you can abort it with Evaluation Abort Evaluation ():

  • The position of the cursor or selection does not affect what is aborted.
  • All computations are aborted, including any that were queued but not yet evaluating.
Notes
To abort a computation in a program, use Abort:
To remove a cell from the evaluation queue, right-click its cell bracket and choose Remove from Evaluation Queue:
  • You cannot remove the current evaluation from the evaluation queue.
  • Some computations in notebooks run automatically. If they take too long, you will get this message:
    If you click Abort, automatic evaluation will be turned off. To turn it back on, choose Evaluation Dynamic Updating Enabled:

    Abort a computation in the Wolfram Cloud by clicking the computation icon in the upper-left corner: