If you want to customize your prompt, might I recommend reading this article
to see what you can do.
The colours for this are a little outdated, but still good on a black-background. Here's the line I put in my .bashrc file:
export PS1='\n\[\e[32m\][\u@\h, \d \[\e[31m\]\w\[\e[32m]\]\n\t \$ \[\e[0m\]'
As for how your prompt changed, it looks like maybe your /etc/profile file went missing...