2000 Buick Lesabre

2000 Buick Lesabre 6 cyl 125000 miles

i have a 2000 buick lasabre the car cranks but wont catch someone read on the code reader computer it came up with anti-theft fuel detterent. He also checked the spark plugs and there was no spark. I spoke to a diffrent mechanic he said this reading is in error it could be a diffrant problem. I checked the module and the coil packs someone said it might be the crank sensor. I want to know if from the symtoms it can be somthing else or it is the anti-theft system and what I should do to fix it, will it help to reflash the PCM.
barry