Jewel Match IV 18

I am probably doing something wrong, but at level 18 I have completed all rooms, and I am in a room finding things to open with a key, this is the last action in Level 18. The hint button does not appear. I cannot seem to go any further if I do not find what that is unlocking. I could not find a specific walkthrough for level 18.

Is the game glitched at that level or am I doing something wrong?

never mind! That last key was to a box inside a box I had already opened!

Glad you got it - sounds like the stomper box prototype HO scene you were in. In case you didn't see the two threads in the forum with spoilers and tips I posted, you can also Google the JM official website and use the left Ctrl + L key trick to find out which actual level you are on, should you get stuck elsewhere and need a walkthrough. Enjoy the rest of the game!

I am stuck on Level 18. The arrow points to a keyhole, but there is no key to be found on this screen. I've blown up, unchained, hammered everything on the screen thinking the key should show up, but after many, many attempts, the timer runs out, my lives and gold are gone, and I have to go back to replay with the same result.
What am I doing wrong?

Welcome to the pond!

Your level 18 may not be the same as another player's since when the puzzles appear depends on how much you do in a level. It's probably that you missed a HOS or puzzle someplace...check the sidebar at the left for available things to do because the keys can also appear in the puzzles.