If this does not help, the configuration register of the router may be set to a non-standard value (not 9600 bps). If you can access the router through a Telnet session, check the value of the configuration register by issuing the show version command. Ensure that the value is set to 0x2102 or 0x102. Reload the router for a configuration register change to take effect. Change the configuration register by issuing the the config-register command.
If the router has not been configured to accept a Telnet session, try different connection speeds.
These are the valid connection speeds for Cisco routers: