Win 7, 32 Bit RC build 7100 won't shut down

Hello I have have this problem since the installation of RC version.

When I press shutdown button, logout works and then computer stays in "shutting down" forever...
I have to shut down computer by pressing Power button 6 seconds... At startup it sometimes tell that computer was unexpectly shutted down and tries to find reason ....

Mobo is Asus M3N78-EM wit Geforce 8300 (720a? + 8300mGPU) chipset.
4GBDDR2 667mhz.
Samsung 2,5" 320GB Hardisk
Hauppauge WinTV-Nova T-500
Alink USB Wlan stick
LG multi DVD drive

I think reason might be USB related but I am not sure. I have installed latest drivers for chipset and upgraded latest Bios for mobo.
In mobo backpanel there is stack of 4 USB connector marked with red colour. and they don't work. If I put eny USB device in these, windows tries to install driver and fails.

In device manager everything is ok with usb ports.

In event viever I can find only notifications that computer has recovered from unexpected shutdown.
Is there a way to find out in events or other "debug" what driver couses the freeze?

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