Hi Bazvinda, welcome to the Seven Forums.
Your system specs tell nothing else than that you have a desktop PC. This normally means you are using an external display (as opposite to laptop's internal display), so this is most probably an issue in display's own adjustment settings. To confirm this, please see the screenshot below and do this:
- Press and hold on the title bar of any window you have opened maximized (buttons hidden beyond the right edge)
- Drag the window down a bit to restore it (last non full-screen windowed mode), then drag it again to the top of the display to maximize it
If the same happens and buttons disappear beyonf the right edge, the display's own adjustment settings are wrong. It might also be due missing or faulty driver
(video card on PC or monitor). If however the windows settles now normally as it should, filling the screen and buttons visible, we have to think something else.