We had an issue at work this morning on the front end web server, as always I usually delve straight into the log files, this is what I find:

0x2498  ULS Logging                              Unified Logging Service              uls1      Monitorable       Tracing Service lost trace events.  Current value 13. 

I found in a forum post on MSDN that when this happens, you need to restart the Windows SharePoint Service Tracing service.

SharePoint immediately started logging the events appropriately, so. In summary. Im still not sure what the initial problem was (I shall have to look elsewhere) but found out something I didn’t know. The beauty of SharePoint.