ORA-01113: file 5 needs media recovery ORA-01110: data file 5: '/usr/lib/oracle/xe/app/oracle/product/10.2.0/server/dbs/databases/mdsdfdata.dbf'
prueva a recuperar el datafile:
SQL>conn / as sysdba connected. SQL>recover datafile '/usr/lib/oracle/xe/app/oracle/product/10.2.0/server/dbs/databases/mdsdfdata.dbf';
o
SQL>recover database;
finalmente puedes probar de forzar el arranque:
startup force;