Well,
The most important (and maybe only, i dont know) change in LW Pro is that it has no ads.

Wont stay connected means that all hosts your LW is trying to connect to dont accept incoming connections. Go to your connections tab and check it.

The only way to solve this problem is to add more bootstraps.
Go to options and add those servers to your list (router.limewire.com should be already entered).
public.bearshare.com
connect1.gnutellanet.com
connect2.gnutellanet.com
connect3.gnutellanet.com
connect4.gnutellanet.com

This should do the trick