are you using a desktop app or a Windows Store (Metro) app? the Windows Store app should automatically bring up the keyboard.
the desktop app doesn't. for the desktop app, you're going to need to right-click on the taskbar and go to toolbars and then enable the Touch Keyboard. then when you bring up your desktop app, just tap the touch keyboard icon.
my new vivo smart tab is doing the same thing, however this happened after tablet froze and I had to reset to factory. Now when it goes through the start up screens I can only get as far as 3rd screen where it asks to "name your tablet" but the keyboard will not come up so I can't type anything and it will not let me go any further. I have also tried pusing the "reset" button on side - same results. Any help would be appreciated!