Hi! Thanks for your fast answer !!
I did remove ALL of the LW Pro ; throw away the install.pkg, repair authorisations, checked disk. Réinstalled a "normal" version 5.1.3 but still no effect. The icon bounces onces and that's it. I tried to move the Java in their preference file : nope;
The only change between yesterday and this morning was the apple Java update. Yesterday LW worked perfectly, after update it doesn't even want to launch...

I'll try the beta version and let you know.