cannot run rake

I am new to ruby. When i try to run rake, my dos prompt just closes
and it terminates the application.
All I did was create a demo app ( rails demo) .... cd demo .. change
the database settings and then do a rake.

Please help.

You have to open the dos window first, then run rake.

Start -> Run -> cmd

Otherwise the window just closes because it has completed the task you gave it.