Does it crank? You if so, you need fuel, air, spark and compression.
Fuel: After 5 years you will need to drain the fuel tank and put fresh gas in it. It will take time for the fresh fuel to work it's way through the system. Your fuel filter might be clogged. When I changed mine on my 05 4.0 the dirty side drained something that looked like used motor oil. PITA but not really that hard.
Air: Get a shop vac, open up the air filter box, vacuum out any loose crap and replace the air filter. You may want to remove the entire air handler and check to see if the throttle can still move. Wouldn't hurt to remove and clean the throttle body.
Spark: pull a spark plug wire off the plug and have someone crank it to see if you can get a spark to jump from the connector to the plug. Your coils might need to be replaced. After 20 years you may as well replace the plugs and wires, too. OEM are best and coils wires and plugs might be due anyway.
Compression: If the other stuff doesn't work, how complicated to you want to get?
Before you get into that, you will want to check to make sure any hoses or wires are aren't loose. You could have multiple vacuum leaks on a 20 year old engine, too. Did you pull any codes off the computer? There may be a doozy or two hiding in there as well.
