can not save cisco config

can not save cisco config

whenever I reboot router, the configuration was gone. 

I am looking for the way to save my configuration... 

Problem... 

Router#show version 

Cisco IOS Software, C870 Software (C870-ADVSECURITYK9-M), Version 12.4(4)T7, RELEASE SOFTWARE (fc1)

Technical Support: http://www.cisco.com/techsupport

Copyright (c) 1986-2006 by Cisco Systems, Inc.

Compiled Wed 29-Nov-06 00:43 by kellythw

ROM: System Bootstrap, Version 12.3(8r)YI3, RELEASE SOFTWARE

.... (omitted... )

Configuration register is 0x2142

Router#

Solve....

1. Type configure terminal , and press ENTER.
2. Type config-register 0x2102, and press ENTER.
3. Type end, and press ENTER.