If this fails to solve the problem, swap cables or test the console cable you are using. This is done by attaching the console cable to the console port of another router.
The console line speed on the router may have been altered. The configuration register of the router may be set to a non-standard value for which the console connection speed is higher than 9600 bps.
Access the router through a Telnet session, and check the value of the configuration register by issuing the show version command. Ensure that it is set to 0x2102 or 0x102. Reload the router for a configuration register change to take effect.
Change the configuration register by issuing the config-register command. If the router has not been configured to accept a Telnet session, try different connection speeds.
These are valid connection speeds for Cisco routers:
Once you have gained access to the router, change the line speed to the default setting, as shown:
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#line con 0
Router(config-line)# speed 9600
Once you change the console speed, you lose connectivity. Go to your terminal program, change the baud rate to 9600, and reconnect to the router console, as shown:
Router #write memory
When hardware replacement is indicated, choose from one of these options:
If you have a hardware support contract directly with Cisco for this part, use the Service Order Submit Tool to request a replacement part directly.
For warranty service, contact the Cisco Technical Assistance Center (TAC) directly at 1-800-553-2447, or online by using the TAC Service Request Tool.
If your product is not covered by contract or warranty, contact your Cisco partner or reseller to request a replacement part for the hardware component that is causing the issue.