Check your IP address using ipconfig and compare it with the address in your Simconnect.xml.
For some reason my PC IP address changes every now and again and I have to edit the Simconnect.xml to reflect the changed IP address to get Simconnect to work again.
Trevor
There's a slider setting in Aircraft Tab of the Display Settings for 2D Panel Transparency, its probably set itself to 100%. Just reduce the slider to 0%. That should fix it.