When PyMOL crashes, 90% of the time it is due to exhaustion of available RAM. Sometimes you will get a message like this in the output:
*** EEK! PyMOL just ran out of memory and crashed. To get around this, *** *** you may need to reduce the quality, size, or complexity of the scene *** *** that you are vieweing or rendering. Sorry for the inconvenience... ***
Other times, the operating system will simply kill the process leaving the user with no indication as to what actually happened.
Generally speaking, the only solution for memory exhaustion is to get more RAM and/or switch to a 64-bit build (if using a 32-bit build).
However, if the problem is happening during raytracing, then you can try to set hash_max to a lower value, such as 80 or 100, in order to reduce RAM usage. Depending on what representation is being shown, you may also be able to reduce certain settings such as cartoon_sampling or surface_quality in order to reduce the sheer amount of data being rendered.