ho cercato nel file .err e ho trovato questo messaggio:

100320 15:23:46 [Note] Plugin 'FEDERATED' is disabled.
100320 15:23:47 InnoDB: Error: unable to create temporary file; errno: 2
100320 15:23:47 [ERROR] Plugin 'InnoDB' init function returned error.
100320 15:23:47 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
100320 15:23:47 [ERROR] Unknown/unsupported table type: INNODB
100320 15:23:47 [ERROR] Aborting

100320 15:23:47 [Note] C:\Programmi\MySQL\MySQL Server 5.1\bin\mysqld: Shutdown complete