Without knowing more:
1. Check the crash directory and see if a crash dump was placed there. The numbers will correspond to the logfiles they go with.
2. Check your logs in the log dir. See if the very end of the most recent ones has any indication of what was happening.
3. Read up on GDB and use it to examine your core file if it still exists.
If that's not enough - post with as much detail as possible. Indicate what you were doing when it crashed, any messages that hit the screen before it happened, that sort of thing. Ask your players if it crashed and you didn't cause it. The more details you provide the more likely you are to have it solved.