Welcome to the forum!
I have seen symptoms similar to this, when people report that they are using a 2 or more monitor setup. Usually I've heard about it with Macs, but not always. Or I've seen it with unusual screen resolutions, or switching the screen orientation from landscape to portrait.
For the tooltips, in Windows versions before 10, you can change the font, size, color, etc. I don't know exactly how to find those settings on Windows 8. But if you've never changed them, I would lean more towards it being a problem with Inkscape. Are you able to see tooltips elsewhere in Windows, or in other programs?
What is that theme you're using in Windows 8? It doesn't look the default theme. Could it be a classic theme, or high contrast? I haven't heard of any Windows theme which causes a problem with Inkscape, so mostly I'm just curious. But I still wonder if it could be part of the problem?