The first thing that you need to do is to get an external monitor to perform this job.
The following steps are to reinstall the KSS:
1 - Power off the controller and wait for it to completely shuts down
2 - Plug the external monitor into the KRC PC on the cabinet door, it could be Displayport or DVI port.
3- Power on the controller, now the monitor will show the window login screen with the default user and password you can search around in this forum.
4- Go to Minizie HMI in SmartHMI Menu, in case you can still boot the KUKA HMI, where you can get the Windows screen.
5- In the window system tray, there is a green icon of the robot, right click and select stop KRC.
6- Run the setup.exe in the directory D/Krc_release and follow the steps to reinstall the KSS.
Kuka is recommending reinstalling the KSS but we never received a recovery stick.
Did you buy one? Robot does not come with one. These little things are not cheap and you have to order them from KUKA. IF you don't have one, you can ask if someone near you has one... But stick alone is not enough. That is just tool used to transfer image to and from robot... So you need KSS image for your system.
