Fixing Magento’s admin panel
Several times now I have had issues with the Magento admin panel not working as expected. In almost all of these cases the solution has been to simply upload all the core code files again, overwriting what's there. This is about as brute force an approach as I can imagine – using a hammer instead of a surgeon's knife if you will – but it seems to do the job in most instances. I recommend doing this as one of your first troubleshooting steps.