You should make yourself a folder somewhere in home or My Documents or similar (not in Program Files) and put all your Java work there. If you open a command line, then write mkdir java, then cd java, and you are straight into your folder and can find everything.
Using the "dir" or "ls" commands allows you to see whether your .class file actually exists.
The error message suggests you have in fact set up your PATH correctly, so don't alter them. Did you get any compiler errors?
Don't set a system classpath at all at this stage. If you set a system classpath in the last 24 hours, you have done it wrongly. Have you installed any programs which might have set their own classpath? You may find it easiest to add .; to the beginning of the classpath.