Router Booted to Weird Prompt

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I have a two Cisco 2500 routers in my practice lab. My lab lost power and the routers rebooted. One of them came up with this prompt:

When I type h I get this listing of commands:

h

$ Toggle cache state B [filename] [TFTP Server IP address | TFTP Server Name] Load and execute system image from ROM or from TFTP server C [address] Continue execution [optional address] D /S M L V Deposit value V of size S into location L with modifier M E /S M L Examine location L with size S with modifier M G [address] Begin execution H Help for commands I Initialize K Stack trace L [filename] [TFTP Server IP address | TFTP Server Name] Load system image from ROM or from TFTP server, but do not begin execution O Show configuration register option settings P Set the break point S Single step next instruction T function Test device (? for help)

Deposit and Examine sizes may be B (byte), L (long) or S (short). Modifiers may be R (register) or S (byte swap). Register names are: D0-D7, A0-A6, SS, US, SR, and PC

Does anyone know what causes this? Also, how to get back to normal i.e., booting and loading my config from NVRAM?

Thanks