Check to see if your problem is related to known issues with your browser version, above.
Clear your browser's cache.
Clearing your browser’s cache may help to resolve problems such as trouble using drag-and-drop features, or trouble viewing the gradebook. See Clear Your Bowser’s Cache.
Try a different browser and/or move to a different computer.
You may find it helpful to have more than one browser installed on your computer. If you run into problems using Moodle, moving to another browser may resolve your issues. You can also try moving to a different computer to see if the problem persists. This may help to discern whether your issue was a problem with your browser or computer, or with Moodle.