Hey guess what, you've encountered the wonderful world of buggy Microsoft programming.
Was the system left running? Was OE left open? Did the system crash or reboot? Did someone touch your stuff and now won't admit it?
Look at the files in the location where OE stores your mail. (You can find the path in the Options under Maintenance.) See how big the files are. If the inbox.dbx file is only a few KB, then you're hosed. If it's still large, you MIGHT be able to recover the files but I don't know how offhand. Just make sure you don't do something like "compacting files".