P1212, P1610, P1612, U1000, U1001, P0462.

P1212 is a supplementary restraint code. Is the air bag or seat belt light on?
P1610 may be the issue for the no start. It is a code that indicates a failure in the security system. Most commonly, the problem occurs when an uncoded key is used. If the security light is solid with the key on, engine off, the ECM has detected a problem and most likely it won't start.
P1812 is a specific Nissan code which indicates a security sensor problem. Check for a burning smell around the radio area. I have seen coins slide into that area and cause a short in the AC amp.
U1000 This is relating to the same thing I mentioned. I feel something has caused the AC amp to short.
P0462 is when the PCM recognizes the fuel sensor signal is too high or low. Gauges will usually not work or provide false readings.
U1001 is a communication fault. Most likely tied into the other issues listed above.

I believe you have more than one problem. I believe the no start is related to the issue with the security system malfunction, but I need to know if the security light stays on solid KOEO.

The other issues can be tied with the cooling fan staying on. I believe something has shorted with the air conditioning automatic amplifier. On more than one occasion, I have seen coins fall behind and cause a short.

It's funny that this problem is starting to show up. It's just a poor design. Tell me, is everything working properly now?