In this case, the file system on the device from which the CPU tries to load the Cisco IOS Software image is corrupted.
Depending on the router model, choose from these resolution options:
If the router platform is c1600, c2500, or c5200, it eventually loads the boot image.
If the router platform is c4000, c4500, c4700, c7200, c7500, or AS5800, ideally it eventually loads the boot image as well unless the bootflash is corrupted.
This is an example of what the prompt on the router looks like:
Where Router is replaced with the hostname of your router.
In order to resolve this issue, perform these steps:
On low-end platforms, there is no need to format the Flash.
Note: Do not save the configuration while in boot mode, because all the information about routing, such as static routes and dynamic routing protocol configuration, is lost.
If the router is a c2600, c3600, or AS5300 series, it falls into ROM Monitor (ROMmon) mode. Use these options in order to resolve this issue:
Note: The ROMmon variables that have to be configured are case sensitive.
If the router is a c4000, c4500, or c4700 Series and falls into ROMmon mode, refer to ROMmon Recovery for the Cisco 4500 and 4700 Series Routers.
If the router is a c7200, c7500, or AS5800 Series and falls into ROMmon mode, refer to ROMmon Recovery Procedure for the Cisco 7200, 7300, 7400, 7500, RSP7000, Catalyst 5500 RSM, uBR7100, uBR7200, uBR10000, and 12000 Series Routers.