Help: Arduino is installed at win7 / 64 Bit... But i dont receive Incomming Data

Help: Arduino is installed at win7 / 64 Bit... But i dont receive Incomming Data over Com.Port...

With severel other PCs most 32 Bit Windows it works...

What do i wrong? In the Device Manager the Arduino Uno is diplayed as Arduinoi Uno. I could install the driver without problems...
But with Firmata i dont receive anything at COM-Port...
Thank You!!!