Alright so I have an 03 civic ex. One day it just decided it wasn't going to start anymore. When the key is in the ignition I get the warning sound that the key is in and that's it. Windows won't work, mileage doesn't appear on dash. Radio doesn't turn on, fuel pump doesn't kick on. Dome light and headlights work. I replaced ignition switch and checked grounds. Even put in a new battery. Any ideas?

 

Did you check all of your fuses and the connection to the ECU?

 

I think, the only reason you could get a warning sound the key is in the ignition is if a door is open. (close all doors)

Does the 03 civic have a main relay like my 91 crx si?
(check the wiring diagram)

Does the check engine light come on when you switch the ignition to ON (don't go all the way to START)?
three possibilities:
-no check engine light at all (power to ECU or bad ECU)
-check engine light comes on an stays on (get an ECU code reader and find out what the ECU thinks is wrong)
-check engine light comes on then goes out after a short time (ECU is functioning correctly)