There are times when files just refuse to open. When this happens to you, the first thing that should come into your mind is the Registry. The registry is the database where all the settings and options for Windows are stored. When there is a corrupted or missing registry file, the computer may fail to work properly. Video files are the usual files that do not open sometimes. There are many types of video files and each type has a different file extension. The registry stores information about which application plays a particular video file. For example, those that have file extension QTL are associated with Quicktime. The .qtl (QuickTime Link) file extension is associated with QuickTime movie files located on a web server, and available for users to download or stream. File extension QTL has the same exact format as .mov file. You can even change the file extension qtl to .mov and still be able to play it. If you cannot open file extension qtl, probably there is a problem with your registry. The registry must always be kept clean and organized to ensure that every program works and every file loads up when called upon. Try A quick scan with Driver Detective can usually solve the problem. You can check out this software at FileExtensionQTL.com.