Why Does My Router Lose Its Configuration

When your Cisco router finally boot up, enter to the privileged mode in order to execute a commands and check the current confreg value. 

When you type show version and press ENTER you will receive the configuration registry value. If the value is 0x2142 it means that the router bypasses the startup configuration stored in NVRAM during its boot sequence. 

In order to resolve that issue, you have to replace that value on configuration registry with the 0x2102. 

From the Router# prompt:

1.     Type configuration-terminal , and press ENTER.

2.     Type config-register 0x2102, and press ENTER.

3.     Type end, and press ENTER.

To verify the configuration register change, type show version at the Router# prompt, and review your show version command output again

When the router is reloaded, the new configuration register setting becomes active.