Either the truck isn't getting sufficient spark or fuel, sometimes air. There are many many reasons your truck may not be starting. It would be wise to have it looked at by a professional to determine the issue and provide you with an estimate and warranty. We would be very happy to be of assistance so you can drive your truck again!
RepairPal Certified shops can diagnose and repair your 1999 Lincoln Navigator. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.