After not using my 2005 Audi A6 for a whole month my battery died, and I charged the battery and it didn't start, I bought a new battery and it won't start either. It shows in the screen that

nothing... everything inside the car lights up, that's the only response I get. nothing... everything inside the car lights up, that's the only response I get.

It may require one of the following things.
1. Since you got your lights to turn on, there is still some voltage in their, just not around the 12 or so required to start your car. You may need to just jump start it, and let your alternator charge it up, make sure you drive it for awhile, idling won't charge it.

And/OR

2. Check the nut/bolt on the positive terminal. Sometimes these become lose, especially if you've had to disconnect for electrical work sometime prior. Make sure it's nice and tight, and that not corrosion is around either of the terminals. To remove corrosion, take a quarter of a can of coke and baking soda, put into a cup you can throw away (although be careful, because it can eat away at plastic cups) then take an old toothbrush, dip in the solution and wipe down the terminals. Then spray the terminals with a battery protectant solution that you can buy at your local auto supplies dealer. also it might actually have what's called an engine lock. (The User's Manual will let you know if you have one and how to unlock it.) The lights will come on, etc., but the car won't start. It'll just make a clicking noise. also If its manual put in the clutch when you try start. If its automatic put it in Park. It may require one of the following things.
1. Since you got your lights to turn on, there is still some voltage in their, just not around the 12 or so required to start your car. You may need to just jump start it, and let your alternator charge it up, make sure you drive it for awhile, idling won't charge it.

And/OR

2. Check the nut/bolt on the positive terminal. Sometimes these become lose, especially if you've had to disconnect for electrical work sometime prior. Make sure it's nice and tight, and that not corrosion is around either of the terminals. To remove corrosion, take a quarter of a can of coke and baking soda, put into a cup you can throw away (although be careful, because it can eat away at plastic cups) then take an old toothbrush, dip in the solution and wipe down the terminals. Then spray the terminals with a battery protectant solution that you can buy at your local auto supplies dealer. also it might actually have what's called an engine lock. (The User's Manual will let you know if you have one and how to unlock it.) The lights will come on, etc., but the car won't start. It'll just make a clicking noise. also If its manual put in the clutch when you try start. If its automatic put it in Park.