为什么会一直Could not find the main class

新下的JDK1.6版发.环境变量这样设的.
classpath=.;%JAVA_HOME%\lib\dt.jar;%JAVA_HOME%\lib\tools.jar;%JAVA_HOME%\jre\lib\rt.jar
java_home=D:\jdk1.6
path=%JAVA_HOME%\bin;%JAVA_HOME%\jre\bin

CMD里输java javac 有命令出来.但是输java version出来一串代码.Exception in thread "main" java.lang.NoClassDefFoundError: welcome
Caused by: java.lang.ClassNotFoundException: welcome.class
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Meth
at java.net.URLClassLoader.findClass(URLClassLoader.java:1
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.jav
at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.jav
Could not find the main class: welcome.class. Program will exit.

用javac编译这段代码可以编译.
public class wel

打开电脑就会弹出Could not load:FNGMHLIB 为什么装软件时出现could not initialize installation...... 为什么有时候显示could not find the macromedia Could not copy we could not help___ Could not reserve record? could not find the macromedia could not initialize language setting could not load jvm .dll I could not bear it.