iTunes sharing features issues only with my newest desktop

Hi, hope someone will find an idea about my strange issue

I migrated my iTunes Library on my more recent desktop (OS Windows7 64 Ultimate)

I still have an old desktop (Windows XP Pro 32) and a laptop (Windows Home Premium 64)

My 2 desktops are plugged with CPL (and a switch)

My laptop is either wifi or direct lan to my routeur switch

All of them are authorised in iTunes.

My iTunes Libs from old desktop and laptop are always seen between my iOS devices, my laptop, my old desktop

My main iTunes lib migrated to my most recent desktop is either seen and shared by all my devices, pc

OR... on this desktop it becomes impossible to share or to see other shared library (both shared libs and home shared libs)

it happens when iTunes starts. From the beginning, if sharing works, it works all the time.

If sharing doesn't work, I found a way to make it come back temporarily :

- with iTunes still opened, I activate another network card (for instance my wifi receiver which is disabled by default)

- I close iTunes

- I desactivate my main network card (it's a Realtek from my mainboard)

- I cross fingers

- I restart iTunes

in most cases all my shared libs / homesharing come back. I can see shared stuff from other pc, and i can share to all my network. Then, I activate my Realtek network card and I desactivate the wifi one. Sharing still works.... Until another time when i start iTunes and there is no more sharing features.

Last clue : when i use an app like remote linked to my lib, then I close itunes, then restart, and in the case sharing seems to not work after that, sometimes remote is able to work whereas the library is not broadcasted on my network ... in appearance !

Any idea ? any similar cases ?