Solution for ORA-01157

Recently while dropping the database some of my other datafiles gone missing. Because of this when trying to open the database got an error "ORA-01157 - Cannot find lock for the file D:\oracle\Oradata\Oradesigner\Designer" and the database is not at all opening

Solution
1. Login to database as / as sysdba
sqlplus > connect / as sysdba
SQL*Plus: Release 9.2.0.8.0 - Production on Thu Feb 8 14:54:38 2007
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to an idle instance.
sqlplus > startup mount;
ORACLE instance started.
Total System Global Area 236404368 bytes
Fixed Size 724624 bytes
Variable Size 201326592 bytes
Database Buffers 33554432 bytes
Redo Buffers 798720 bytes
Database mounted.
sqlplus > alter database datafile 'D:\oracle\Oradata\Oradesigner\Designer' offline drop;
Database altered.
sqlplus> alter database open;
Database opened

Changing the Default Gateway using Command prompt

The command is:
to change IP and default gateway:
netsh int ip set address "local area connection" static 192.168.0.101 255.255.255.0 192.168.0.254 1

to change DNS:
netsh int ip set dns "local area connection" static 192.168.0.254 primary

This is assuming 3 things.
1) The network adapter you're trying to change the IP for is "local area connection". It could also be "local area connection 2" or "wireless network connection". Look in your control panel for the correct name
2) The IP you want to set is 192.168.0.101, change this to whatever IP to want to use.
3) The default gateway and dns are the same IP. If you are using some kind of router they usually are. Change this to match your network config found with the command ipconfig /all

You will need to run both commands to change the IP.