Set PC ip_ddress:

pc: ip address : 192.168.0.2
subnet mask: 255.255.255.0
default gateway: 192.168.0.1

And then Power on the router:

hit Ctrl + Break key together. And the router will appear:

rommon 1>
Then type the following commands:

format              Format a filesystem-format <filesystem>

format flash:

IP_ADDRESS=192.168.0.1
IP_SUBNET_MASK=255.255.255.0
DEFAULT_GATEWAY=192.168.0.1
TFTP_SERVER=192.168.0.2
TFTP_FILE=c850-advsecurityk9-mz.124-6.T5.bin
TFTP_CHECKSUM=1

rommon1 >tftpdnld
When you see “!!!!!!!!!!!!!!!!!!!” running, you’re successful and wait some minutes until progress finish.

fsck                Check filesystem consistency-fsck <filesystem>

fsck flash:

If you have the output of a show stacks or show tech-support command from your Cisco device, you can use
the Output Interpreter to display potential issues and fixes.

dir flash:

set = display the monitor variables

rommon 16 > set
PS1=rommon ! >
TFTP_TIMEOUT=800000
FE_SPEED_MODE=4
TFTP_RETRY_COUNT=20
BSI=0
RANDOM_NUM=1540763391
CRASHINFO=flash:crashinfo_20020301-000015
ROM_PERSISTENT_UTC=1014940815
RET_2_RTS=
RET_2_RCALTS=
%