Hyundai Veloster Engine Not Running

First Off It Reads That It Is Still In Reverse Second You Can Turn The Car On But It Will Not Start All The Lights Come On Radio Etc., All...

If I Turn On The Ignition To Start The Car, I Hear It Trying To Start But Takes A While (10 Seconds Or So), Sometimes It Won't Start, So...

My Vehicle Has 133,000 On It. Battery Tested Good By Mechanic About 2 Weeks Ago. Only Three Years Old Battery Diehard Gold. For Some Reason...