Could you send a screen shot (or even just a photo) of what you're seeing? Does anything "work", or do you just see two green squares and nothing responds to blocks or mouse clicks?
It is quite possible that it's a Java issue, but it also may be a graphics driver issue. Sometimes going to the manufacturer of the graphics card (e.g. Intel, AMD, Nvidia) and getting their driver directly solves the issue, if the driver you're using came instead from the computer vendor (e.g. Dell, etc.).
Best,
--Daniel (StarLogo TNG/Nova lead developer)
p.s. I have to ask - is there anything in particular about Nova that you don't like, or that you miss from TNG? We're still actively developing it, so there my be an opportunity to incorporate your feedback.