Making a message box when process cannot be found.

Hello, I'm creating a process manager kind of like task manager and I'm trying to make a new task button. What his does is open a new form and in that form has a textbox and a button (and some other labels that are not relevant). The textbox name is Text_ProcessStart and when you hit the button it executes this command line Process.Start(Text_ProcessStart.Text). That works perfectly fine, but if the process cannot be found the program gives me a fatal error. I want to make it so if the process can't be found on the computer, it will create a message box. :)