URGENT: Dashboard Non-responsive

I’m having serious issues with my WP dashboard – it seems many functions are non-responsive.
1. Cannot access media library when creating a page/post (click the button but nothing happens)
2. Cannot drag widgets around or access dropdown thingy to edit them (dragging results in text selection across the screen)
3. “Screen Options” and “Help” tabs at the top right of the dashboard do nothing when clicked
4. Cannot switch between HTML and Visual Editors
5. Hovering with the mouse over the various tabs on the left (Posts, Media, Links, Pages…….) doesn’t reveal the sub-menu

and much more… my dashboard is practically disabled…

I tried everything I knew before posting here and nothing worked. I’ve read around and searched for solutions with no success. Here’s what I’ve done so far:

– reinstalled wordpress core files
– made sure javascript is enabled in my browser
– cleared browser cache
– tried multiple browsers (IE, Chrome, Firefox) – same problem with all
– configured all file permissions to 644 and directories to 755 on my FTP
– made sure database was fine and wp-config looked alright (although i don’t know much about that…)

I’m really lost here guys I really need some help FAST because critical changes need to be made on my site.

thanks in advance!