How to find a app running in a computer connected in a LAN...

Hi Guys,
I've designed a app that uses Previlages and Security Logins. I need to know, how should I check whether my app is running on a network (LAN). If it is running, then how should I determine on which computer is it running. And How should I send message to that computer in through my app. Because my app includes users like administrators, backup operators, guests and restricted users. If any Problem is encountered then immediately a system alert should be given to the person at administrative level. How can i do this... Any help will be greatly appreaciated. Thanks in Advance. I need your help very urgently please.... :( :confused: