I used the key to open the door of my car and now it won't start I unplug the battery and it still won't start
do you have a key icon showing on your dash during power on? if yes your immobilizer got tripped when you used your key in the door. A simple trick is to try turning the key to power on leave the car for 15 minutes in this mode then flip the key back to off then try starting.
Search Audi A4 Questions
Audi A4 Experts
Related Models For Sale
Used Cars For Sale