Hello, you cannot "manually" turn off warning lights.
And, warning lights being on - in themselves - are not reasons the vehicle will not start.
Sounds like some diagnostic testing is in order to determine why your vehicle will not start, and unfortunately, you'll need some technical help from a shop near you.
Use this link to find some shops near you that can help with your concern:
www.repairpal.com/repair-shops
RepairPal Certified shops can diagnose and repair your 2003 Audi A4 Quattro. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.