Hi and welcome to leJOS. Before posting a new topic please take a little time to browse the existing topics or search the forums. If you do that you will find:viewtopic.php?f=18&t=6945
Which may help you. To use leJOS over USB you must have an RNDIS driver installed. The above thread and the threads it links to provide detail of how to ensure that this is installed. The thread also provides details of how you can test to see if your EV3 is connected (by using ping to 10.0.1.1), and the possible reasons why if ping works you may not be able to auto detect the EV3 (firewall blocking things).
If you have tried the above please let us know with details of the results. Also when asking for help please provide as much detail as possible (like the version of leJOS, what version of Windows - 8? 8.1?, etc.).