This kind of problem is extremely annoying. In my case, CSRHarmonySkypePlugin.exe (part of CSR Harmony drivers for a CSR Bluetooth 4.0 USB dongle) was grabbing Ctrl+ Alt+ Up and Down and a few others - with no UI to configure that or turn off! Sooner or later you should find the offending process. Again, keep checking if the hotkey becomes available. Create Visual Guides with Templates 3 min.

Sort processes by user and start killing user (not system) processes one by one. Introduction to Snagit Library Read Manage the Library Read Convert Your Previous Captures View All Create 4 min. If everything is closed but the problem persists, open the Processes tab in the Task Manager (or better yet, download the Sysinternals Process Explorer). Make notice of what you close and every time (or every once in a while) test if your program (is it Greenshot?) can now use that hotkey. Tips: You can also press Ctrl+C to directly copy AutoHotkey v2 Help. First, close all your running programs (including stuff in the system tray), one by one. I use this all the time when copying some text In this AutoHotkey tutorial I show. I can only offer you the most primitive way of handling this problem.

Sorry I can't suggest an alternative to Hotkey Explorer for Windows 8 or 10.

Snagit hotkey guide