SharePoint is trying to tell you something. Use the ULS viewer to find out what!

Unified Logging Service in SharePoint is great, but you need a way to view the logs. Enter ULS Viewer - a free tool you can download from Microsoft CodePlex in order to debug a SharePoint environment. Keep in mind that it can only log what it receives, so when you have networking problems or even IIS problems that come before SharePoint, your ULS logs won't have much to tell you. But when you've just deployed a new feature or web app and now your having a meltdown, you should definitely take a look using this tool. And the features!

• View multiple SharePoint log files at once
• Search by any field
• Filter the log by any field
• File drag & drop support
• Live monitoring for entire farm
• Export filtered log entries
• Bookmark log entries
• Get popup notification of SharePoint log events from system tray
• Receive email notifications on errors
• Redirect log entries to event log
• Supports SharePoint 2007, 2010 and 2013

System Requirements:

• .NET Framework 3.5
• Windows XP or above

Download the ULS Viewer here: Download ULS Viewer
You will probably want to launch the tool as an admin.
Open the Viewer and from the file menu choose "Open From", then "ULS":

You can reference the default SharePoint ULS logs location or an alternate location:

The Logs will show you what is going in the mind of SharePoint. You can filter to "Show High Messages" which will reference ony high priority errors