I've tried every possible button combination I can remember when it comes to Windows tablets.. Nothing works..whoever figures this out be sure to tell us.
I had a quick search and found this, How to take a screen shot on a Windows 8 tablet without a keyboard - Good Gear Guide Australia
That too doesn't work. What I do is bring up the Charms Menu and choose the Share option . Tap the first option at the top allow you to take a screenshot to share. I just share it to OneNote and grab the pic from there.
1) Swipe from the Right edge to the left
2) Select Share
3) Tap the Drop Down
4) Select Screen Shot
5) Choose the app you want to send the screen shot with
Its the only way I know of as of right now
Press your Windows Button just ahead of your Vol - the screen dims and it's done. Your Tablet will then make a Folder named Screenshots (If it isn't already there), and you will find all your caps there.
we can choose one more option - Chinese name of the installed application.While in an app open the charms bar by swiping from the right. Touch Share, and you should see a dropdown at the top, change this to Screenshot. After that you can choose how to share the screenshot depending on which apps and accounts are set up on your tablet.
The thing is, the Power + Volume Lower button does work on other Windows tablets, but not the Stream 7.everyone must remember this is a tablet, but it is running full windows, not windows phone. Charms bar is the only way I know with out a prtscn
button.