Starting a windows application from a windows service
You cannot start an interactive application from a Windows Service. This was changed in Windows Vista and 7.
Some other advice was given in this Stack Overflow answer on the same subject.
When I've needed to do this, I had to change my Windows Service to a Console Application, and invoked it in that manner.
A work-around I found for this issue was to use the windows task scheduler. You can schedule the application to run some amount of seconds later by creating a batch file.
At my previous company we had this issue and we wrote a console app that ran in the sys tray and acted as a bridge from the service to the desktop. Basically via remoting (I'd use WCF now of course) we let the service request that the console app start up another application.