Hi stonzee! Read below, and I'll explain it to you how I have to do it Sweetie.
Just in case you don't know, after clicking on the print screen button you need to open an image program such as Paintshop Pro, Photoshop, etc / RIGHT CLICK in the grey work area / and PASTE AS NEW IMAGE/ crop it if you want to. / Then save your screenshot as a jpeg or whatever format you choose.
After doing the above if your screenshot doesn't paste it means your F Lock is on and you need to click the F lock button and start over. Hope this works for you. Big hugs!!!!