As long as your database is still in good shape, you can re-upload the entire Power CMS and just make sure to define the connection properly and it will work fine. In fact, that's what I was hoping you could try... it would be like doing a new install except you do NOT need to run the SQL command file. Just make sure your global settings are identical and reinstall all the PowerCMS files - then give it a try. From what it sounds like, there could be number of issues - but the problem with items when you expand may mean the Moo Tool javascript file has been altered or corrupted.
Regards,
Brian