I have a 2003 Neon and my trunk will not open with the key.

I can open it through the latch by crawling through the back seat so I know the trunk is open-able. It's just when I put my key in, it will not turn, as if I was putting a wrong key in a house door lock.

Anyone else experienced this?

 

Try it with both hands, the lock might be pooched, or there could be another issue. Has the key always worked before for the trunk?

 

It happens to mine sometimes.. I couldn't get in my drivers door for a day once. Is that the only lock that does that, if your key is slightly bent it could present some problems..

Maybe the lock cylinder is no bueno.

 

I don't know if it's always been like that because I just recieved the car.

And yes, only the trunk has this problem. The two front doors open with the key with no problems.

 

You could have some corrosion inside the lock that makes one of the sliders stick. That would cause the lock to remain locked.
It's early in the year, so I would suggest a small shot of penetrating fluid inside the lock. Allow it to sit overnight, then see if you can wiggle the key and unstick the slider.

Later in the year, make sure you use a good key lube before the winter weather sets in.

If the lock remains stuck, one of the springs could be broken. They aren't really difficult to take apart if you have a donor lock to use for parts.
See if you can get one (same make and year donor car) from a junk yard to disassemble to familiarize yourself with the inner workings. Then take yours apart and repair it.

 

I live in FL so I don't think weather will do much but thanks for the help.

 

Give it a go then.

I live in upstate NY and winter weather is a consideration for certain things.
My drivers' door had the same issue and WD-40 freed the lock.