Okay, that means the issue is with the computer running a large, long-running model.
Running out of disk space generally creates a different error, but it is good to check that you have space. Freeing up space is easy to do.
One idea is to submit the solution to My Computer, Background. That means Mechanical will submit the job to the solver as a standalone job. Once the solve starts, you can quit Mechanical. You can track the progress by looking at the Solve.out file. Since Mechanical is not running, it CANNOT CRASH! When the solver finishes converging on the final step, you can start Mechanical and retrieve the results.