got audio signal ( hiss) but no mic throughput on 550D <SOLVED>

[pictonaut]

Hi all,

just installed 2.3 and all is smooth so far. I am currently testing the headphone monitoring via the AV cable / mini USB. It shows "headphones connected", and I definitely got a signal output, there is a typical preamp hiss when boosted an little pops when incrementing the boost level steps, the levelmeters react to the int.mic but there is no mic sound coming through. I tried through headphones and a mixing desk, same thing.
Is there something I'm missing?
The one weirdish thing I see is that whith the headphones plugged in, when I disable the headphone monitor in ML, the screen goes black and I have to restart the 550D.
Thanks!

EDIT: SOLVED...
turned out to be a faulty  jack to chinch adaptor.