Bash is the "Bourne Again SHell", a pun on the earlier Bourne shell. It is one of many command-line environments available in *nix systems. Csh, tcsh, sh (the original Bourne shell), and zsh are some of the others.
As trickykid alludes to: you are now, for some reason, booting into a non-graphical runlevel (for Redhat, probably runlevel 3). To fire up the GUI from there, you should be able to type "startx" (no quotes) at the command prompt. Check your /etc/inittab file and check the line which looks like this:
In the case above, the "3" refers to runlevel 3. To boot directly into the GUI, edit the file to change that value to "5".
BTW- What exactly
were you doing when your original configuration changed?