I would be glad to help. It's possible you have renamed your drive, or that your system recognizes it as a different drive for another reason. I would simply follow Apple's directions to transfer your backups from one drive to another. However, since you are still using the same drive, you can skip the section "Copy your backup data from your original drive to your new drive". But in place of this skipped section I would copy your "Backups.backupdb" folder to your machine's desktop temporarily, in case Time Machine doesn't recognize the backups on the drive and erases them. If the backups aren't available after following the instructions, simply copy the folder from your desktop back to your drive in the same location at the root of your drive. and it should be back to normal. The page with these instructions can be found here:
Let me know if you run into any trouble along the way or if any of the instructions are unclear. Also be careful not to reformat your drive as instructed in step one, as this will erase all of your existing backups on that drive. If your drive is not already using the Mac OS Extended (Journaled) file system, we will need to try a different solution all together. Let me know if that is the case, and do not follow through with those directions.