No power when in gear- reverse works fine

The fault occurred shortly after my exhaust fell off?, no visible damage. basically when I start the car and attempt to drive it, there's no power or gears aren't engaging. I've tried a CPU reset, no joy! And there are no fault codes appearing on the diagnostics scanner. I really want my Frontera back in action. Is it a sensor problem, the trans oil is clean and a red/ pink in colour. Any help would be appreciated.