Database mounted.
ORA-00313: open failed for members of log group 1 of thread 1
ORA-00312: online log 1 thread 1:
'C:\ORACLEXE\APP\ORACLE\FLASH_RECOVERY_AREA\XE\ONLINELOG\O1_MF_1_647O6RPP_.LOG'
ORA-27041: unable to open file
OSD-04002: unable to open file
O/S-Error: (OS 2) The system cannot find the file specified.

SQL> ALTER DATABASE OPEN;
ALTER DATABASE OPEN
*
ERROR at line 1:
ORA-00313: open failed for members of log group 1 of thread 1
ORA-00312: online log 1 thread 1:
'C:\ORACLEXE\APP\ORACLE\FLASH_RECOVERY_AREA\XE\ONLINELOG\O1_MF_1_647O6RPP_.LOG'
ORA-27047: unable to read the header block of file
OSD-04006: ReadFile() failure, unable to read from file
O/S-Error: (OS 38) Reached the end of the file.

alter database clear logfile group <group no to which the dropped logfile belongs to>';

alter database open;