Problem opening programs.

Every now and then, when I have a certain something open (it can be anything
from a folder to a webpage), windows just stops accepting certain commands.
It'll switch between the already open programs, but won't acknowledge any
commands to open something new and more often than not will stop accepting
right clicks unless I find out through trial and error which program is
causing it and shut it down first.

I'm using Vista Home Premium (32-bit) on a Dell Inspiron laptop.
Help?