If by CLI you mean the console port then make sure you are using an actual rollover or console cable and it is connected to the console port (and not to any other port e.g. modem port) on the 80C. Use Putty or other serial/terminal connection software. Make sure you are using the correct com(1-7) port in your putty/terminal program -- you shouldn't be getting any error message unless you are using the wrong com port or it is already in use. (If using a Windows-based computer, go into Device manager and check which actual com ports are available.)
Turn off the 80C, connect the rollover cable to the console port on the 80C, start your putty/terminal session. Power up the 80C -- you should see the bios start up sequence. Watch for any errors. It is likely (based on your description of the problem) that the flash is corrupted.
During the boot sequence you should be offered the chance to break into the boot menu. Let it run through once to see what errors show up before or after it reaches the login prompt. Reboot the 80C again, this time break into the boot menu.
If you have not already backed up the config, you could try booting the 80C using the alternate backup firmware option and see if it allows you to get to a login prompt and hopefully connect via the GUI. Otherwise, I would just format the boot device then install a new image via tftp.
I would run the HQIP test next. You can obtain a copy of the HQIP firmware from the download menu option on the support site (after you have logged in). You will need 4 x crossover cables for this test.
If you are not able to gain access to the 80C via the console port or it never reaches[size="2"] "Press any key to display configuration menu..." or you still get errors after formatting/installing new firmware, you will need to open an RMA ticket -- they will want a log capture of your putty/terminal session showing the errors. [/size]
I read i should try restore firmware image by tftp server, but another problem is I cannot connect to cli interface now, I get the message "device is used by another program" or something like that (I guess because it is starting up...). Connection options are correct (9600, 8, 1, none, none), because before I joined up.