Please use the below steps for factory reset. This will surely resolved the issue.
Turn the C20 off by pressing the physical reset button. Now hold the physical reset button for 15 seconds, the LED will start blinking red. Release the button and push it twice within the next 5 seconds (the led will turn green on each push). The LED will start blinking green and the factory reset will begin. The C20 will come up again with factory defaults.
Before you do a factory reset on the codec as suggested by Amlesh, please check the following :
DNS Servers and IP config :
Please check if you have 3 or more DNS servers configured in the codec and the IP assignment is set to static. If yes, then make sure that the DNS servers are reachable. If a codec running TC software is configured with three or more DNS servers and is set to use static IP, it will not boot up if all three DNS servers are unreachable.
whenever the unit reboots it makes a tar file which is a bindle of files containing information about the codec. If you are able to access the codec via GUI, could you check Diagnostics -> Log -> Historical where historical logfiles are stored and download the most recent ones or, depending on the version, you can also have a historical log file bundle you can download with all the files. Open a case with TAC and let the engineer analyse these crashes.
It can be the DNS issue, but without these files, one cannot tell for sure. Might be some other issue.
Upgrading to TC5.1.2 is perhaps the easiest step. If the unit would still upgrade after this, use the procedure above and open TAC case with bundled file attached.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.