Problem with saving files.

Hello everybody,

I'm new here and I'm just using Autocad 2011 for few weeks. I use it  at school, without any problems when I have to save my file, but at home.. disaster..I always receive this message when I open autocad

I click: ok and it starts.

The problem is: when I have to save a file, the programme stops working, doesn't answer any commanmd and what i created new isn't saved.

At first, I deleted the programme and downloaded and installed it again. 

Then I discovered, through  a forum, that there is a command: fidelia, setted on 1 (I can't save anything and autocad stops) and iif I set it on 0 I can save my file, but the command save in in aline, so I can't change the name.

Why I can't use normally ib a windoe?

please help me.

fo rme it's difficult to use the programme and to explain this sort of things in English.

Thanks a lot

Sonia