This error:
The program can't start because sfml-system.dll is missing from your computer. Try reinstalling the program to fix this problem.
is because the SFML DLLs have to be in your project directory
(There is somewhere else you can put them, but that's never worked for me)
EDIT: As for PATH, go to Start and right click Computer. Click
Advanced System Settings on the left, then in the resultant window click
Environment Variables. Finally, in the bottom pane, scroll down until you see an entry named
Path and double click it. In the resultant window, scroll to the end of the entry, make sure there is a semicolon after the previous path and then add your Code::Blocks installation directory (don't put it in quotes).