I encountered a problem with similar symptoms today. I'm not sure if it is the same problem but it matches everything in your question.
In my case, the log files said:
!ENTRY org.eclipse.core.jobs 4 2 2015-12-03 15:49:19.369
!MESSAGE An internal error occurred during: "Launching NewTest".
So my problem was that the TestNG-plugin in Eclipse failed to find the pom-file, as I don't use Maven. Anyway, after uninstalling the optional M2E (Maven...) part of the TestNG Eclipse plugin I could run my TestNG test cases successfully.
If you have the same issue, you uninstall the M2E part in Eclipse by selecting
- Install new software...
- What is already installed?
- Select the TestNG M2E software and click uninstall
Hope this helps!