Goood morning, welcome to JustAnswer!. This is Ed.
Your 2003 Ram was in a transition state between one engine system to another in 2003, so I'll need to bother you with a few questions.
First off, which engine do you have? If you're not sure, just send me the last 8 digits of your VIN and I'll be able to decode it from here.
Next, does the engine crank at all? By that, I'm wondering if the starter engages and spins the engine over.
Did it start first, then die?
Did you have to jump start the truck before this began? Have you jumped it since?
Do you have a spare key? I'm guessing that with the red light flashing in the dash, your truck is equipped with the immobilizer system we call "SKIM". It requires a grey-colored ignition key, one that 's been chipped, so if your key is anything but grey in color, try to find that spare one. You can't start a SKIM-equipped vehicle with a black key.