I am having the same problem - the drawing just suddenly disappears and I have to force quit Autocad to get any response. When re-opening the file, all edits since my last save are lost.

Almost any action can provoke it - selecting a line or hatch pattern, stretching, deleting, etc. Crashes occur frequently sometimes (after only a minute or two), at long intervals at other times (well over an hour). I can't see any pattern suggesting why this variation occurs.

I have tried uninstalling Autocad (which required downloading and installing trial 2015 version first, then uninstalling that), then downloading the latest version of 2013 and reinstalling it, with no improvement.