Not sure if you have figured this out yet. But you need to make sure the switch in the top right corner (by the Microsoft logo) is switched up so it lines up with the blue line. This enables your blue functions that are listed on your top row of keys. It took me a minute to figure out why the heck it wouldn't work either.
Try other possible solutions:
Option 1: Snipping Tool - Windows built-in screenshot tool that enables you to snapshot whole screen or any selected area.
Option 2: Free Screenshot Capture - free and online screenshot application that works fine for taking screenshots, making annotations, uploading and sharing images. http/screenshot.net/
It almost sounds like your clipboard is full and it isn't clearing itself. You can run the command "echo off | clip" (without quotation marks) to manually clear the contents on the clipboard, or alternatively install and run CCleaner to clear the data stored on the clipboard.