my Audi A4 is not starting what can be the problem?

have you tried checking the battery ? normal causes for a car not to start is a dead battery due to a drain or bad cell which is you likely cause need more info for more answers. start from what it does when you open the door till when you turn the ignition. I need to know if the interior lights work when you open the door cause if they dont its a battery issue if not its something else

Audi a4 1.8. The interior lights come on as soon as you open the door. When you put the key in the ignition everything works but when I turn the key over it wont crank but I can hear the relays going. What is wrong with it?

first place to start is battery. anything less then 10.5 volts and it won't crank. lights will still be on but wont turn. If the battery is good check the starter for signs of corrosion on the points wire. if no corrsion give the starter a couple raps with something hard and try it again. if it turns over you need a new starter after this as it ussaly means the points or solioid are sticking

Check ✔ for corroded wire coming off the terminal or fuse?