No main method can be found [FIXED]

Hello everyone.
First of all, I think this post is only for those who are using no IDEs, only the Java Development Kit and cmd.
Ok. I’m having troubles with executing my projects. Yesterday, all worked well. In cmd, when in my project’s repertory, when I wrote

java <class containing the main method>

, all worked fine and the project ran. But… Now, it won’t open the project (even those I had done before) using the command, saying I have no main method that can be found. It seems I have to do

java -cp "%cd%" <class containing the main method>

:-
One change I have noticed is that the

echo %CLASSPATH%

command returns “null” :o Before, I’m sure it was something more like “%classpath%;c:\Users etc”. Moreover, no matter what I set it to (with the

set %CLASSPATH%

command) its value won’t change :persecutioncomplex:
I’ve tried installing Java again and it changed nothing. Could some charitable god help me out of this now ? :3 Thanks a LOT !
J0