I am running QGIS 2.18.15 on a Windows 10 OS 64-bit PC and the click symbols to close (x), minimize, restore, maximize are missing. I tried uninstalling and reloading the latest version and had same problem. I can use the keystroke commands but it is impossible to resize the window that way. In order to move the QGIS window between screens I must also use the keystroke commands - cannot drag between screens.
Everything else seems to work fine.
Am just wondering if this is a common problem and if there is a fix.