Error with uploading Asset Files: net::ERR_EMPTY_RESPONSE
That usually means "something fatal happened" when trying to upload the file.  The usual culprits are the php.ini max_execution_time and memory_limit settings, but if it's happening for small files too, something else could be going on.

Have also seen it happen when you're uploading an image in a format your underlying image processing library doesn't support.  i.e. your server has GD installed, but you're trying to upload a 32-bit PNG.  Or you're running an older version of GD or Imagick that has a bug you're hitting.

Check if you have a craft/storage/runtime/logs/phperrors.log file.  Any PHP fatal errors will be logged there.  If not, then check the Apache error logs to see if it's an Apache problem.