Application can't startup?? Solaris and Linux RedHat

can someone tell me what could cause an application not to startup? I'm getting calls from users saying they cant' startup a particular application. how do I troubleshoot this?

i tried doing ps -ef | grep (application)
i saw the application running. now, am wondering, would it be safe to send the application a kill -HUP signal and then ask the user to try restarting the application? or what could I possibly do in this situation??

check the log files (if the program is generating them)

ask the users what if any error messages they are seeing, and yes, as root kill the application and then have the user restart it and see what happens. actually first your better off running it your self so you can better troubleshoot the problem.