ULS Viewer no items

I had the problem, that when I started ULS Viewer, no items where displayed. Then checking the 14-hive of SharePoint and the log folder, all log files had 0 KB size. When checking the SharePoint log-settings, everything was set properly. The problem was, that the disc space ran out. I cleared the disc, so I had at least 1,2 GB space. I restarted the SharePoint 2010 Tracing (Windows) service. Then I deleted all the old 0 KB files in the log folder and voila, logs were written to the files and ULS viewer could display them.