Had this problem happen a while ago and it took me forever to figure out how to fix it. I eventually realized it was because I was using a keyboard shortcut I wasn't aware of. Had people randomly ask if I knew how to fix this problem, so I'm assuming this is pretty common.
The Issue - Stage is locked at the top left and you can't pan. The Fix - View > Pasteboard or Ctrl+Shift W
The Issue - Was starting a new project and soon into it I noticed that dragging stuff leaves an outline of the object instead of dynamically showing the actual object. Looked online but couldn't find much about it, which is probably because it's a real simple mistake.
The Fix - To avoid it, make sure to pick actionscript 3.0 when starting a new doc. Copy over everything into that doc if you're far ahead into it, but I doubt you get that far without getting annoyed by this issue.