I got a 7 year old aosmith water heater and it wont fire up it has a itelli- vent gas value the innighter is on but noflame

SOURCE: dripping from drain spout

If you are refering to the "Dripping coming from the preasure tempature valve,Then just turn off the valve where the water goes into the heater and open the P/T valve with a bucket below it draining only emought water to get below the level where it reaches.     Normally the drain valves are plastic with a Male hosebib attached.  Attach a  garden hose to the rain and run it out to a point lower that the vaslve in order for gravity to drain the tank.The valve opens counter clock wise. If the valve is stuck or does not drain,and you have a foor drain handy,remove the whole valve and replace it with a boiler drain valve.  If The tank is located below the drain level then you will have to either pump or carry the drain water to the higher level.     Replace the P/T valve  and reinstall the associated associated piping. I would use tefelon tape on the P/T pipe theads.    You may have to open a hot water faucet in order for the air to replace the water in the tank ,in order to drain. 

SOURCE: Eractic Power Vent Gas Water Heater

Th epproblem you are most likely have is from a safety called a flag switch usually located either in the blower or right past it. When you unplug and replug you reset the switch. Sequence of events.  1 fan comes on. 2 switch is made from the airflow of the fan.  3 ignitor come on 4. main gas valve opens and ignitor starts flame. 
You are being stopped at step 2 when the fan does not move with the air. This shuts off and out the water heater from calling again.  Find the fan switch and make sure it moves easily. They get dirty and also dry from lack of lube. Good luck.  

SOURCE: Rheem 40 gal power vent gas water heater shows code 42

you plugged it in and the fan started or you unplugged it and the fan started,,the fan will come on first before the unit will inginte to take out the excess gas, if it didn't lite then the ignitor might not be working there are 2 swithces on the unit one on the fan and one by the gas valve make sure they are both on and make sure the gas it also turned on.

SOURCE: Can I Use Existing Venting from Old Water Heater?

Late answer to an old post, but no you can't use the existing vent pipe. The tankless systems require Category III vents along with all the accessories required for your installation. I suggest you use a direct vent model with the concentric vent through the wall. Remove and patch the roof penetrations of the old vent or just abandon and let it remain.

SOURCE: Loud blower on my new Rheem Power Vent 2 water heater

find out if it does the same noise with the venting disconnected