No start 1996 chevy Blazer

I don't think 3 months makes stale gas, maybe year old gas, but not your short time. And if not mistaken, I think you have throttle body injection on an '89 chevy, although chevy always was a little behind the curve on new improvements to cars. hint, hint.
The computer has everything to do with it. it controls ignition timing, it controls spark, it controls the fuel pump and the injectors. Since it won't start with starter fluid or gas, next step is to look into the ignition system. Check for spark on a couple of spark plug wires. If you have a blue, snapping spark, you can assume your ignition system is working well enough to start the engine. Take a spare spark plug or pull one of your plugs from engine, attach the plug wire onto it, and lay the plug on a metal piece of the top of engine-the spark plug hex and threads is the natural ground for the plug, so if you lay the threads on a metal piece, or hold it tight against a steel bolt, you can observe the spark jumping the gap, and no danger of getting shocked. But if you hold it, just in case, wear a glove or wrap a heavy cloth or rag around the wire. Remember, a blue energetic spark has to be seen to verify good ignition. Oh yes, you need a helper to crank the engine over while you watch for spark. If no spark, and you have a distributor, check the coil wires output at the end that connects to center top of distributor.Pull it from distributor and hold the metal end terminal no more than 1/4 inch from a ground source, a bolt or the frame, or an engine bracket. Helper has to crank the engine over, and watch for good blue spark. If no spark there-ignition: coil, crank position sensor (or maybe a pickup coil inside your distributor-same function), ignition control module, computer, and all the associated wiring.
If coil has spark, but none at plug wire ends, inspect closely the distributor cap and rotor. not passing current or shorting out there.
So the basics are, to run, the engine needs gas, air, compression, and a timely spark.

Faulty fuel pressure regulator.

I'm following another issue like this on a 1996 Jimmy.
This engine requires 60psi or more fuel pressure to run.
You need to have someone check the fuel pressure at the rail- throttle body with a gauge.

Could be the fuel pump is not providing the proper fuel pressure !
Fuel psi less than 50 psi no start GM CPI Vortec

You may have a fuel pressure problem or the secuirty system has locked you out for some reason due to a false signal or failed part. Do you have any electronic engine control codes? Is the Security light on in the instrument cluster and fishing when you try to start the truck? To check the fuel issue get a can of spray starting fluid from the auto parts store or any hardware store and spray it into the air intake of the engine while someone cranks the engine, if it starts you may have a defective fuel pump, the pump is located inside the fuel tank, the fuel tank must be removed to access and replace the pump.

Have you sprayed fuel/starting fluid into the engine to see if it starts? You can have fuel pressure but no injector fuel delivery, we call this "pulse"

starting fluid is a thing of the past. dont use it. this car doesnt have a carb, its a throttle body/ electronic fuel injection system. you most likely have a fuel pump or fuel pressure regulator issue. test the fuel pressure, should be anywheres from 35-50 psi

My first thought would be: If you repaired an emissions hose, take the car back to Auto Zone (or another parts supplier) and let them tell you what code comes up now. You eliminated one problem, now you have to find another.
I wouldn't do a fuel pump without more information.
Gary

Check for gas or spark problem on the engine. Check that starting fluid does start the car for a few seconds before dying, indicating a fuel delivery problem, like a fuel pump or circuit to it.

If the car won't start with starting fluid sprayed into the intake, then the ignition system may be at fault, or engine timing.

It could be your fuel pressure regulator, check this link for details:

http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c1528022b9c4

That's what it looks like.