Black screen is caused by java not loading, this can be caused by one of the following:
Using Firefox with a very outdated java (can be fixed by downloading a new version of java at Java.com) (firefox disables java that is outdated for protection reasons).
Having java disabled manually (you have do enable it manually again).
Having an outdated and wrong java enabled (check your browser plugins or java settings) to check which java version is enabled and which is disabled.
So easiest fix would be download the newest java version at java.com.