system user locked after crash

Hi, we have an application running with OracleXE 10g on Windows. It's not unusual that the application runs in the same pc which host the db server.
It happened that, after a sudden crash of the system and after the windows reboot, the Oracle system user was locked.

Ok, now i've unlocked the user but still don't know why this happened. I can only imagine a series of wrong user/pwd connections, but it seems this isn't the case.

Thanks in advance for any answer to my doubt

--
francesco pighi