I love this car but now it's dead and I don't know what to do I definitely need help
 

I desperately need help with my 07 maxima sl the spark plug tube seals were bad so I replace the valve covers after the swap it ran great way better than he did prior only for about 20 minutes and then it just died no warning no sputtering no anything it just up and died and I tried cranking it over and it would not fire didn't even try to start it ran great before I did the swap it it ran excellent afterwards I don't know what happened I was careful to hook up everything the way it was hooked up before but I noticed after it died that I forgot to hook up the sensor that's on the left hand side next to the front valve cover I also noticed afterwards that the thermostat gauge was no longer working Adam had work before and unfortunately right after I cranked it over the second time after it died I pulled the key out and now the ignition doesn't work anymore I tried charging the battery thinking that might help and that didn't help at all I was able to get the steering wheel unlocked by turn the ignition just enough and wiggling it to unlock it but the lock cylinder still will not go to the on position or the ACC either I don't know what to do a little background information I paid 400 bucks for the car 6 months ago I have the steering knuckle replaced I had the right bearing replaced I had to sway bar replaced and the tie rod ends .someone took the catalytic converter prior to me purchasing it but I have to be able to put a pipe in to quiet it down its a very nice car and I got a screaming deal on it I love the car

You didn't mention anything about the key fob. Do you have any? Did the car fail to start with or without the fob in the car? The sensor you forgot to replace was probably the Engine Coolant Temperature Sensor since you said the temperature gauge was not responding. You did not mention that you had the SES light on. Surely it would have been on with a sensor not connected.