YOU HAVE EXACTLY SAME PROBLEM WITH ME
here's my symptom.
Installed Java SE Development Kit 7u5, x86 (newest version)

and the test shows that java runs properly.
(it says java's working properly.)
but i can't run hnh by any client(default, ender, arksu, etc)
when i run default client it always stops here(same as Experimax said)

and ender

totally black(can't even close the window. i closed it by finishing process javaw.exe)
arksu doesn't even start. after dos pops up the client starts and closes itself in about 3seconds
i've got this problem since i reinstalled Win7 OS on my computer.(also formatted.)
is there anyone who got the same problem with me?
or anyone who solved this?