Auto restarts AFAIK are due to Graphic Card issues, viruses or CPU issues. You haven't told us much about your system so it makes it a bit hard.

LW & Java can use a lot of resources & so puts whatever problem it is into ignition mode so the problem with your comp becomes apparent. Chances are that if you were using another heavy duty program it might also incite the problem to show itself. It's most likely a hardware issue or incompatible/out of date drivers for the hardware. Recent graphic card updates have been known to have problems. Your problem might even be due to poor interfacing b/w hardware components.