I've seent this problem before and it should be solved in one of the following ways:
Alternative 1: Set taskbar to autohide by right-clicking the taskbar, choose properties and then check the "Auto-hide the taskbar" box followed > OK, then perform a reboot.
When the OS is rebooted, uncheck the box then reboot.
Alternative 2: Set taskbar to autohide by right-clicking the taskbar, choose properties and then check the "Auto-hide the taskbar" box followed > OK, then perform a reboot. Then right-click the toolbar, choose Task Maanager > go to details > Right-click Explorer.exe > Click "End Task".
Then click File in Task Manager > Run > type: Explorer.exe
Now uncheck the box then repeat the process.