Windows – MySQL 4.1 crashes with “Database was not shut down normally!”

From time to time my MySQL 4.1 Windows service is crashing with the following lines inside the log:

091218  9:31:25  InnoDB: Database was not shut down normally!
InnoDB: Starting crash recovery.
InnoDB: Reading tablespace information from the .ibd files...
InnoDB: Restoring possible half-written data pages from the doublewrite
InnoDB: buffer...
091218  9:31:33  InnoDB: Starting log scan based on checkpoint at
InnoDB: log sequence number 2 817025450.
InnoDB: Doing recovery: scanned up to log sequence number 2 817025450
091218  9:31:35  InnoDB: Flushing modified pages from the buffer pool...
091218  9:31:35  InnoDB: Started; log sequence number 2 817025450
C:\Programme\MySQL\MySQL Server 4.1\bin\mysqld-nt: ready for connections.
Version: '4.1.14-nt'  socket: ''  port: 3306  Official MySQL binary

100107  9:02:51  InnoDB: Database was not shut down normally!
InnoDB: Starting crash recovery.
InnoDB: Reading tablespace information from the .ibd files...
InnoDB: Restoring possible half-written data pages from the doublewrite
InnoDB: buffer...
100107  9:02:53  InnoDB: Starting log scan based on checkpoint at
InnoDB: log sequence number 2 953338420.
InnoDB: Doing recovery: scanned up to log sequence number 2 953338420
100107  9:02:53  InnoDB: Flushing modified pages from the buffer pool...
100107  9:02:53  InnoDB: Started; log sequence number 2 953338420
C:\Programme\MySQL\MySQL Server 4.1\bin\mysqld-nt: ready for connections.
Version: '4.1.14-nt'  socket: ''  port: 3306  Official MySQL binary

Those messages are not pointing at any specific problem. What can I do to trace the origin of the crashes?