Well my first question is, why did you just update to 6_20 and not 6_24 as it is current state of the Java VM?
http://java.com/en/download/windows_manual.jsp?locale=de&host=java.com2nd one did you try and use the error console of Java so we can talk about the real problem? if so it would be nice to post the errors.
3rd what Kind of PC do you use? maybe a netbook? is ist 32bit or 64bit, did you check your CPU and Ram load?