Before my 1990 honda civic stopped running I took the gas cap off to use on another car temporarly (Its a long story). Before I removed that gas cap it was working fine I think I left it off for about a week before putting it back on. It wouldn't start the next time I tried to drive it. Does anyone think this is the reason it won't start?

Has there been a lot of dampness? humidity? rain?
Does it try to start or is it like you might as well not even be turning the key (no sound whatsoever)?

It could be. Gasoline is extremely volatile so the gas in your tank may have literally evaporated away since you didn't have a gas cap on it. You may have in fact be trying to start a car with an empty gas tank.

Yeah good question how much gas and what was the weather like?

I have gone months without a gas cap and no problem.
But it should still crank and sound like it isn't getting gas if it is the gas
If it is doing nothing then it is more likely a dead battery or something.

Quality of the gas possibly deteriorated too much. Run through the tests, in Sections A and B of the "Sticky," just the same.

I took the gas cap off for about a week and I didn't ever drive it with the cap off. I live in Ohio so its been below freezing most of the time. The car cranks but won't start.

Txgreasemonkey, what did you mean by running through sections a and b of the sticky?

He meant A. & B. on here

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-46563.html

You could have condensation/water in the tank.
You might try buying dry gas at Pep Boys or somewhere and follow the instructions.
How much gas is in the tank?

My tank is little less than half full. I got spark, sprayed starting fluid into my intake and didn't get a start.

If starting fluid didn't get it firing, it may be an ignition problem. Fuel may be OK.