Why does my key turn everything on but wont turn engine over???

If the internal components of the key which corresponds with the anti-theft system of the vehicle has somehow become compromised and damaged, then yes - it will prevent starting. But you'll have to see a dealership or at best a locksmith to fix this at quite a cost. Other than that, a transmission shift lever (automatic) that is not securely in PARK or NEUTRAL gear will prevent cranking. A battery too low in charge will allow lights to turn on, but won't crank the engine. Testing hands on is needed. www.repairpal.com/repair-shops