Change buffer readonly and meta-x not responding

[leid]

Hello everybody,
I am an emacs newbie and encountered some problems. When I opens a file,
and try to change something, emacs told me the buffer is readonly and
cannot be changed, how should I solve this problem(I do have the permission
to change it).
Another problem is that "meta x" hotkey is not responding, but do responds
in console mode.
Why?

Thanks