I have an 07 Audi A6. I was trying to start my car today and vehicle would only click. On the dash it flashes park brake and also has solid lights of brake, abs, airbag, EPC , and traction control. The parking brake also flashes by the lower shift console. When I'm turning key, the interior and exterior lights also flicker

 

Now I've been trying to start for so long that the clicking is gone and the vehicle is trying to turn over. when I take key out parking brake light remains and flashes

 

I'm going to have to go with a battery issue on this one.

I'd guess that the battery no longer has enough cold cranking amps to turn the engine over fast enough to effectively start it, even though it has enough power stored to power some of the internal electronic components in the cabin.