window too big, can't resize or maximize
When a window is bigger than the resolution of the monitor do the following:
Press and HOLD ALT (On Ubuntu 18.04+ Hold SUPER) and then simply click and HOLD the mouse button over the window you want.
Start dragging it until you can see the top part or at least a corner to resize it. Keep holding the corresponding key while doing each click until you can see a corner or the top. From there just resize it as you like.
Try this: Alt+F7 and then you can move the window, so you can reach the button :)
I had the same problem on Ubuntu 14.04 in Unity. I solved it by deleting all of the config files for kate. I found them under home/USERNAME/.kde/share/config.
WARNING: this will also remove any custom highlighting, colors, etc. when you do this.
This answer is a bit detailed version of Ffoeg311's.
Just rename the file kritarc(something like kritarc.old or kritarc.backup or may be anything) or delete the file kritarc which is in the path /home/USERNAME/.kde/share/config/. You can leave the remaining files.