It does not matter much whether you use an activity or sequence diagram. Your problem is probably that you did not step out of your application world. The restart is issued from a place outside your application in the operating system. There you have some task manager or whatever it's called which is responsible for concurrently running applications. That is a process of its own. At some time it starts your application (either due to some user interaction or based on some other event). Now you have your application process being created and running. At any time the OS can send some kind of signal to that process. This is different between the OSs but basically you have some exception handler automatically compiled in your code that accepts the signal and exits. Otherwise the OS has means to abort a process without being nice. Showing all that stuff is usually not meaningful (except you are in a OS class teaching people how it works).
Long story short: if you really need to show the restart, stick to something simple. In a SD it would be the creation of your app by the OS and the final kill. Similarly you can show a forking process creation and termination in an AD.
Thanks for help, your comment helped me to reach a solution. I used a "found message" in SD as crash/shutdown and then ended the activation and for restart similar message to app with activation box created again on lifeline .