Terminal commands

Hello to everyone,

I'm writing for an advice, currently i using a MacBookPro with SnowLeopard: i was using terminal commands from several months;
Then i tried to install Gromacs, unsuccesfully,a simple program; From that time i cannot type on terminal: open or sudo or other command; also trying to open a texteditor with Emacs i get:
-bash: emacs: command not found

Do you know what happened to my Mac?
All the best
Alex

Can you open Terminal at all? If you can, what is the output of:
echo $PATH