Boot aborts halfway through

Hi,

Just installed Ubuntu 8.10 on a somewhat older machine (2003 Dell desktop,

previously running WinXP). It gets through startup and prompts me for my username and password, but after that, I only ever get an empty black or offwhite screen with noting but my mouse on it. At that point it continues to recognize the mouse but the keyboard always appears disabled. It never loads anything further.

It probably goes without saying that I'm not exactly a computer expert. Anyone have any ideas about what my machine is doing and how it can be fixed?

Thanks.