Sometimes in the SharePoint LOG, you can get the following information and nothing else:
Service lost trace events.
This happens when the Windows SharePoint Tracing Service is halted or not working. Usually you can just restart the service, but sometimes it won't work. The you can try to run TaskManager and end the process called "wsstracing.exe".
If that is not going to work you can restart the Internet Information Server or the whole Server.
But sometimes it is not possible - in the production department when you need the information of some actual error.
In this situation I use great tool called SPTraceView. This tool will attach itself as online listener to the SharePoint ULS and will capture the errors and messages for you. You can just run it and there is no need to restart the server or IIS.