My 07 maxima has absolutely no power. Ignition switch freestyles when it should be locked. New battery but nothing comes on. Prior to this I discovered i had am exhaust leak/cracked converter. What could be the problem?

 

What does no power mean in terms of RPMs and speed? Do you have OBD codes?

If you mean that you press the throttle pedal and the engine does not rev up, that's a bad throttle pedal position sensor AKA accelerator pedal position sensor. I had this issue in my Quest. The solution was to open up the sensor case and re-solder the joints between the white PCB and connector pins.

If you are in a limp mode, i.e. the tranny stays in 3d gear and does not go over 30-35 mph, than you might have a bad camshaft position sensor. There are two, the code will tell which is bad.

Need more descriptive information about your loss of power.