Commands are entered into a terminal, also called a CommandLine Interface or CLI. It looks a bit like the DOS prompt in Windows. The Aspire One uses Linpus by default, IIRC, you can get a terminal with alt+F2.
It is puzzling that it should vanish like that. Looking around, I see it is fairly common with the linpus lite that the netbook comes with. Acer's standard advise seems to be a full system recovery. The gnu/linux netbooks are still something of a mixed bag and vendors don't quite seem to understand what free and open software is all about just yet. So we are seeing a lot of funny issues like this.
I suspect you'll find the netbook-ubuntu nicer to use.