Two ways to fix this depending on the answer to this question: Are you able to view the emails in the folders that you are dragging them to?
If you can see the emails in those folders, I'd recommend that you close out of Outlook, and run SCANPST/SCANOST on your mail folders. Those utilities would be in your Office directory under Program Files.
If you cannot see the emails in those folders, open the Account Settings box from the File menu, go to the Data Files tab, and verify that the data files referenced are where they are supposed to be. If they are, close out of Outlook, and run ScanPST/ScanOST on them.