SHUTDOWN: waiting for active calls to complete

1. connect to SYS user with new terminal window

SQL> conn / sysdba
Connected TO idle instance.

2. shutdown database with ABORT option

SQL> shutdown abort;
ORACLE instance shut down.

3. open database for normal shutdown with RESTRICT option

SQL> startup restrict
ORACLE instance started.

Total System Global Area 167772160 bytes
Fixed Size 788496 bytes
Variable Size 149682160 bytes
DATABASE Buffers 16777216 bytes
Redo Buffers 524288 bytes
DATABASE mounted.
DATABASE opened. 

4. now shutdown database with NORMAL option

SQL> shutdown normal;
DATABASE closed.
DATABASE dismounted.
ORACLE instance shut down.

5. You can now restart your instance properly.